Board Thread:Warhammer 40k General Discussion/@comment-25149066-20140730083800/@comment-24944355-20140814233804

Only six of the fallen primarchs became demon princes - Angron, Lorgar, Perturabo, Fulgrim, Mortarion & Magnus. Of the others - Horus was killed by the Emperor, Curze committed suicide by imperial assassin & as for Alpharius/Omegon one may have been killed but it's possible both still live but neither became demon princes & no one has any certainty as to what they have been up to.