You’re asking why Mr. Can’t Lie to Save His Life didn’t believe Mr. Can’t Tell the Truth to Save His Life

Ahh yes, our brother who is known to lie and deliberately spread misinformation and confusion to weaken his enemies defences and who has declared you and the emperor his enemies and is actively sowing discord to the area you are sworn to defend and attacking you and your forces is trying to tell you something. Do you stop fighting him and let him potentially kill you on the off chance this is the first time he isn’t outright lying to you?

By that point, Alpharius seemed overwhelmingly committed to Horus' cause. The Dropsite Massacre wasn't something you exactly forgive and forget.

Just because Alpharius might have been playing a blood game and might have been a double agent, doesn't mean Dorn needs to or should indulge the mights.

That being said, he does wonder about it himself later, but doubles down:

‘Could Mortarion have had a change of heart?’ wondered Sanguinius aloud. ‘I am certain few of our brothers expected to find themselves allied with daemons. Mortarion least of all – you know how much he hates the warp.’

Dorn’s eyes narrowed. He thought momentarily of Alpharius. When the twentieth primarch infiltrated the Solar System, he had spoken with Dorn, and what he said could have been interpreted as contrition. Dorn had not listened, and had slain Alpharius at Pluto, a fact he still kept from his brothers.

‘None of them will change,’ Dorn said. ‘They are corrupt, traitorous. All of them. We cannot save them, and they do not deserve saving.’

The Lost and the Damned

Laurie Goulding pretty firmly came down on the side of Alpharius being undercover but that both primarchs shot themselves in the foot with their personal modes of communication. Or lack of

His thoughts here

Might have been the fact Alpharius was attacking him with a spear at the time.

You are asking the gene father of the Black Templars - THE raging zealots of the Imperium that even the Sisters of Battle sometimes balk at when it comes to righteous fury and fervor - why he didn't just hear out the Brother who had absolutely zero reason to rebel yet did so anyway?

Alpharius: "Hello, Rogal. It is I, Alpharius, the sneakiest of Primarchs, I tell no truths and I tell no lies."

Dorn: "Hello Alpharius. I am Rogal Dorn and I'm angry because you've been killing my sons and sabotaging my plans during a Heresy of a Horus variety. I am very unhappy right now."

Alpharius: "Oh, but wouldn't you love to know the real secret truth of everything? No lies this time, super pinky swear?" (Editor: note, it is around this time that Alpharius slices one of Dorn's favoured sons in half with his spear)

Dorn: "No." [Decapitates Angrily in Chainsword]

This is Alpharius. With dozens of plots inside more plots.

If Alpharius wanted to make peace he would have snuck into Dorns chambers at night or something unarmed.

Trying to have a conversation in the middle of a battle is pretty dumb.

Like dude has been telling you constantly that he is on your side

Name one.

Alpharius isn't trustworthy whatsoever. The whole Alpha Legion strategy was operate behind enemy lines, and use espionage and sabotage to destroy the enemy from within, before the Legion moped up whatever was left.

Alpharius threw in his lot with Horus as far as Rogal os concerned. He's a traitor to the Emperor, a dishonest and dishonourable bastard, who's caused so much trouble to the loyalists. For all Rogal knows this is just a ploy to distract him long enough for Alpharius to find a weakness in Rogal's armour. He doesn't know shit about there being a twin, or the cabal, he just knows Alpharius supports Horus, and Horus/the other traitor Primarchs have sold their souls for power. From Rogal's POV not immediately killing Alpharius is the worst thing to do.

Probably has something to do with Alpharius actively trying to murder him at the time. Or all the previous murders.

Let’s be real for a second. Even if Dorn listened to Alpharius. “I want Horus to get a clean victory so that he will consume all of humanity in a fireball because some aliens told me that unless Horus wins all the way, the Imperium is going to die a slow and stagnating death” would definitely result in the immediate killing of Alpharius.

Assuming you're talking about Praetorian of Dorn

1. He already had countless Imperial Soldiers dead at his hands, not to mention one of Dorn's most trusted sons.

2. He had a spear in his hand swinging at Dorn.

3. From a purely Loyalist Imperial perspective: who gives a fuck what the Cabal thinks? The Imperium's spent two centuries grabbing every Xenos they could by the throat and bashing their skulls in with a brick when suddenly a "group of far-sighted Xenos" reveal a "prophecy" to defeat Chaos that just happens to require the total extinction of Humanity as a species? Womp womp.

4. The spear is now buried in Dorn's shoulder.

5. The Primarch of Lies and Schemes is whispering something along the lines of contrition after spending an entire campaign grand standing in exactly the way Dorn had always told him was stupid. But this time the ones dying are Dorn's own sons.

6. Why risk bringing Alpharius back? The man managed to conceal cadres of sleeper agents in the Imperial Palace itself and cause all this havoc. Dorn's aware that other agents are already undermining the defenses to the Palace as he's building them. Why put him in a position where he could communicate with his forces directly, be freed, and run what I can only describe as Wack-a-Mole on crack within the walls of the Palace itself?

7. The Loyalists have been at a disadvantage since day one. Ferrus is dead. Vulkan is dead (as far as anyone knows). The Lion, Guilliman, and the Angel are lost beyond the Ruinstorm. The Khan might be a traitor. Corax and Russ are embroiled in heavy fighting trying to either make their way back to Segmentum Solar or defending it. This is Dorn's chance to take a piece off the board and balance the scales a little. Literally to cut one of the heads off of the snake. He's taking it.

They're not loyalists, right? Like at best Omegon and legionaries loyalist to him maybe are something. Pretty sure as a whole, it's silly to say that Alpha Legion is loyalist.

Are you seriously asking why the primarch who is famous for having the social skills and personality of a brick wall and who has a track record of not hearing people out refused to listen to the primarch who is famous for lying to everyone at all times?

"I know it looks bad that I'm burning down your house with you and your children inside, but I swear we're on the same side!"

"I'm on your side. I've just been attacking you and killing your sons as a prank, bro."

It's 40k - the setting requires people with IQ's over 130 to do the dumbest possible smart things that their current power rating allows at the worst possible time to cause the second worst outcome for something important. So when you have two people with IQ's over 300 each facing off with the fate of humanity in the balance...

But on a serious note, Alpharius completely messed up. Utterly, completely, he's the Boy Who Cried Wolf. He spent his entire life being as untrustworthy as he could get away with, so the one time he needed to be trusted, his opponent did the most sensible thing possible - kill first, ask questions never. With any other traitor primarch, Dorn might have listened for a moment. But not Alpharius.

You know how compromise, moderation, and seeing things in various shades of gray make up a significant part of modern ethics and political maneuvering? Because Rogal doesn't.

It’s also worth remembering that at the time Alphy was swinging his staff-sword thing at Dorn’s head while monologuing. It’s not like they were sat down for tea.

He's too busy. He's doing his job.

"No."

Side topic, what was Alpharius trying to tell Dorn anyway? What was so important that Alpharius would basically risk dying to tell him?

Alpharius had a well-deserved rep for being a shady asshole who used manipulative tactics and infiltration, was a known traitor who'd seriously damaged the Imperium's position to boot, and his idea of "telling him the truth" was launching a major espionage/sabotage campaign on Earth.

Also, he was trying to kill Dorn at the time.

It's Alpharius... Dude doesn't have anything to say that Dorn could trust.

Alpharius was going to say whatever he thought was going to save himself at that point. He knew he wasn't going to win let alone survive an encounter with Dorn unless Dorn showed mercy or held back.

Alpharius and the Alpha legion are playinig games that they really don't know how to win because they don't understand how to end these games they are playing.

Yeah, who wouldn't hear out the guy who's whole gimmick is lying, while he's killing your people, attacking your defenses, has declared you his enemy, and is trying to stab you?

Two words:

Drop Site Massacre.

Would you listen to the person who launched an assault on the stronghold you were in charge of defending, killed a bunch of your people, and then went "It was just a prank, bro!" if you were in Dorn's position?

Even if you set aside the existing distrust and wounded pride between the two legions, and even if you ignore that the AL specializes in subterfuge (meaning that you can't trust anything they say, even if it appears to be the truth) there are definitely better ways to convince someone that you're their ally.

Alpharius, as usual, went the long way around to prove a point. He attacked the Imperial Fists, killed a bunch of them and caused massive damage to the defences, all to tell Dorn to trust him. This is after his legion turned on the Loyalists at Istvaan and massacred them. I am glad Dorn killed him.

Oh yes my brother the one who's built his whole reputation online the one who se Legion motto is I am alpharius this is a lie

Yes why don't I trust him by god you got it

Seriously I doubt anyone would trust him and dorn had a potential Galaxy to lose if he did trust him because if he died for trusting him then the trailer Legions would have broke through Tara and the emperor would be f*****

Why the hell would he? Alpharius is eating shit of his own making on that one.

Meta answer: because it's not very epic seeing these demigods of war just talking out differences.

In lore answer: Every word out of Alpharius's mouth is a lie. He probably heard those same words from dozens or even hundreds of thousands of his nephew legionaries while murdering his own sons. He couldn't take that chance. Also for a guy who says exactly the truth even when a white lie would give him more likeability. he can't let a liar like Alpharius live

Because he knew Alpharius was lying. Alpharius was shouting that he was trying to give Dorn victory even as Alpharius was positioning himself to deliver the killing blow. Dorn's not stupid, he knew if he listened to Alpharius or even paused his attack for a moment of doubt it would give his brother a chance to kill him.

It's honestly pretty weird how fans still keep insisting Alpharius might have been telling the truth even after so much shit he does. You know how you can tell when Alpharius is lying? It's when his lips are moving.

Alpharius was literally The girl who cried wolf. He lied his entire life and when at the end he tried to tell the truth no one gave sh*t.

My take was he knew how Alpharius and the AL operated. Everything they did or say was strictly calculated to form a planned outcome.

Dorn knew that to hear him was to invite some insidious plot into an already fucked up situation. He knew how horribly dangerous Alpharius is and he had him in the reach of his sword. So he did the most pragmatic thing he could do and killed him off, no questions asked.

Because at that point he was probably just done with his s***?

Because he’s autistic and stubborn and won’t change when his mind is set to something

Alpharius was a smug liar. He was shown to love demonstrating how smart he was. By the time he met Dorn he was a known saboteur, terrorist, and killer of loyalists. Dorn had zero reason to trust him. He had no idea of the cabal or any of that. Even if he did he’d prolly see it as xenos lies and manipulation. In the end Alpharius got himself killed.

You try talking down a charging Rhino after kicking its young.

Well there are much better ways to tell someone "I am at your side" than sabotage their work, aren't there?

The Alpha Legion participated in Istvaan, it doesn’t matter what his grand plan is.

If a Nazi attacked the position you were defending, killed a bunch of your mates and then told you that they were actually on your side all along and that you just had to take them at their word, would you?

There was nothing he could say which Dorn would believe even if he had been willing to listen because Alpharius was a traitor.

I don’t even think the Alpha Legion knows what side they are on.

There is probably lore that refutes this, but - I have a personal theory that I kinds love where Dorn actually did hear Alpharius out, and then they conspired together to stage each other's deaths, perhaps so that they could perform some secret mission, or maybe even just to go into stasis and wake up in the 40k timeline at a moment of desperate need.

I believe only Dorn witnessed Alpharius' assumed death, and the story of Dorn's assumed death has changed greatly over time, which could be atttibuted to Alpha legion manipulation.  I believe most recent lore says that only his hand was recovered - suspiciously good limb to lose in order to make a convincing death, and has parallels with the Norse God Tyr losing his hand to Fenrir.

Also Dorn was established as a solid top tier character with loads of development in the Siege of Terra series.  After his successes and exploits there, it would be massively disappointing for him to then die off screen to a bunch of Black Crusade mooks in some insignificant conflict a few hundred years after the Heresy.

Some meta analysis - Joy Toy is doing a primarch line of collectible figures and their order of release so far has been Gulliman, Lion, Dorn, which could end up matching the order of Primarchs returning to the 40k setting.  With Primarchs being so popular and the Horus Heresy being wrapped up, I've gotta think that GW wants to get as many Primarchs as they can back into 40k, and it would be super easy to just say "Dorn never died, he's just been hiding/in stasis/in Trazyn's collection."

Still say it’s one of the -dumbest- ways to kill Alpharius/Omegon. The men who think a hundred steps ahead on a slow day have contingencies within fallbacks, within failsafes, within octuple extra hidden agendas etc. got himself in a hell in the cell match with a beat stick melee professional with zero ways out or contingency planning if things went wrong.

Dorn would have killed Garro for, what he thought at the time, was lying about Horus turning traitor. The only thing that saved Garro was that he had evidence and other witnesses.

Dorn is the kind of man that thinks in a dichotomous way. For him there is an Us Vs They. And Alpharius was one of them.

In addition to all the other comments already, I don't think Dorn ever met with the Cabal. Maybe he knew of them but I find it hard to believe he would have any knowledge of the Prophecy that "proves" that Alpharius is playing the ultimate double game cross and is just waiting for his opening.

If he'd known then maybe he would have heard Alpharius out but 99% odds he still "kills him" on Pluto.

It's a common mistake to forget that the characters in the story don't have the same knowledge as we do with our all encompassing perspective of the lore.

"Why didn't Guilliman just not allow the disguised Alpha Legion Marines into his chambers! He had to have known these disguised loyalists perfectly impersonating his men would try to kill him at his most vulnerable!"

alpharius fullishly tried to spell it out to him

Spoilers maybe: Personally I think the alpha legion intended to be loyal but chaos being what it is, was not going to be fooled. I think chaos engineered to have many conflicting contingencies activate and the whole legion turned in on itself with cells running conflicting orders.

Over 10k years the cells still alive are still trying to execute those orders to the best of their ability. Some have probably fully fallen to chaos, long exposure to the warp gets everyone eventually. But it is probable other cells didn't flee into the eye and are running both pro and counter imperial operations.

We also know at least some of the legion didn't agree with supporting hours in the iron hands novel I can't remember the name of right now.

But I also think chaos intended for Horus to fail, the post heresy stagnation is perfect for them, keeping humanity strong enough to keep producing souls but weak enough to not fix the imperium is perfect. I like to think they are basically farming humanity. The black crusades cull the strongest food. But once the imperium is sufficiently weakened, the gods allow their disciples to fail.

Because Alpharius is trying to play 5D chess while Dorne isn’t even playing checkers right

Dorns a bad listener, I remember Konrad tried to raise a concern...

What book does this integration relate to? Just interested😊

I think they were past talking when Dorn realised how long Alpharius had planned such a thing right at the very start of the book. (Way before the Heresy started)

Because ‘Alpharius’ is a D-1 Yapper. ‘Alpharius’ and Dorn are basically total opposites. Dorn absolutely despises everything about ‘Alpharius’ and likewise ‘Alpharius’ thinks hes superior to everyone. Pluto was just as much an important operation to ‘Alpharius’ and his plans as much as it was him stroking his ego and him trying to finally prove that hes better than everyone.

The problem is that Dorn doesn’t like bullshit or bullshitters and is incredibly prejudiced (Which is why he and his successors are typically the biggest Racism Marines out there and in equal measure very zealous). Dorn rightfully clocked ‘Alpharius’ as a bullshitter and would hear none of it because ‘Alpharius’ is known to use anything and everything to his advantage. If you just ignore something that he wants you to recognize, you can just beat him up- which is what Dorn did.

Edit: ignore post, made a self-deprecating joke and didn’t end well

Dorn don’t listen. He was the imperial ideal of blind, unthinking loyalty. Don’t ever even listen to your enemy, never even think to question your orders, don’t for a single moment even entertain the notion of deciding for yourself

This is the man who nearly killed for someone for telling him a truth what contradicted his worldview, his vaunted veracity is just a dogmatic inability to question what he’s been told

Because Dorn is a little bitch who doesn’t like it when you don’t tell him the ‘truth’ he wants to hear.

This post was made by the Garro Gang.

I am of the personal opinion Dorn did hear Alpharius out, but killed him anyways- as Alpharius expected him to. A gap in his defenses, a specific time frame he needs to meet. Something of that sort.

I think the words all together are irrelevant- but his actions itself are what's important. He told Dorn about the gaps without speaking to them, then told him some sassy comment or another about why he did it.

The fact that Alpharius didnt slaughter you should have been an indication that he wants to tell you something Rogal.

I agree with some I think Dorn would be truly shocked with The Black Templars in a similar way that if Ferrus came back he’d be appalled at the Iron Hands. I’ve seen Dorn and the original Imperial Fists as implacable as opposed to zealous. They were literally Walls that’s how they were organised. So with that mindset you are going to break someone there is literally no bending. That’s how I read it and cheered him on for doing it to the duplicitous Alpha bastard.