After the Heresy one of the two primarchs was said to have been killed by Guilliman , the primarch of the Ultramarines , but knowing the Alpha Legion 's frequent lies and dissent , no one knows if one of them really survived or whether both survived .
After the Heresy one of the two primarchs was said to have been killed by Guilliman , the primarch of the Ultramarines , while another may have been secretly killed by Rogal Dorn on Pluto . 
 However , knowing the Alpha Legion 's frequent lies and dissent , no one knows if one of them really survived or whether both survived .