Board Thread:Warhammer 40k General Discussion/@comment-6078851-20130130174042/@comment-3258762-20130213164714

I think Alpharius asked nicely.

Seriously, I think Alpharius explained the benefits of keeping Omegon secret from any and all and the Emperor saw the sense in it and kept it secret. The Emperor was not one to be fooled by all the "Astartes never fight one another!" crap, he had killed off the Thunder Warriors and had had at least one legion censured, almost certainly having included killing too loyal Astartes who refused to see their Primarch dead. And, he might have forseen that one of his sons would betray him and that having a second primarch unknown could be a boon to him.