Originally Posted by
TOTALITY
It’s #4 of the current volume by Chip Zdarsky.
I would assume it’s after Xavier met Moira, since POX shows that occurring around Xavier’s earliest ideation of his grand place in the world. I assume the war was pretty soon after meeting Moira and his experience with Namor sometime after that, but I don’t have a firm sense of when he met Magneto. Seems like he had a sort of “world traveler” phase that’s endlessly ripe for new flashbacks, and a lot of them could occur in any order without making much of a difference, Namor among them.