Who Killed Alpharius

Did Dorn killed Alpharius?

Finally, Dorn finished off Alpharius with a deadly chop of his mighty Chainsword into the top of his brother’s skull. With the death of their Primarch, the Alpha Legion fleet withdrew and retreated from Pluto.

Is Alpharius still alive?

alpharius is dead. it was in the praetorian of dorn book where he was killed. it was omegon replacing alpharius at the end. as for whether or not guilliman killed omegon that is still up to debate but it is more likely than not that omegon was killed at the great scouring that followed the horus heresy.