Board Thread:Warhammer 40k General Discussion/@comment-14745711-20140911102114/@comment-6078851-20140912134918

i couldn't remember who found them, so horus and emps were the only ones outside the legion who knew they were twin primarchs.

there were only 20 gestation capsules: from what i've read it seems emps created 20 embryos but one of them split, as embryos have been known to do, to produce twins. although emps was surprised at this as he wasn't trying to make twins.