basically what happened was apocalypse transferred his consciousness into charles in the pyramid fully, like he planned to. and all the xmen and horsemen gather and erik sees charles for the first time and is already regretting everything- but hasn't fully grasped it all yet... until charles-apocalypse does a little mind thing and all of a sudden all the xmen are on the ground, screaming, rolling around in pain, and holding their heads (except jean cuz she's kool and has ~mind powers~ but she's still using her powers to block it out and also like rightly freaking out so no phoenix powers yet). it's seeing this monster wearing charles' face, smiling as he hurts/is killing his friends, that erik has his "what have i done moment". and raven is not just screaming incoherently and in pain, but erik's name, so erik is like okay loml please stop hurting them??? and apocalypse is like hmm??? bitch look this one's your son (cuz either charles already knew or ya know can just reads minds) and he's like hey peter tell him you're his son and peter's just like owowow and so apocalypse increases the mind shit he's doing and is like tell him he's your dad but also tell him to kill you and all the pain will stop and so peter's like hi dad please kill me. and erik's like no tf and tries to kill apocalypse instead but can't because apocalypse is too op so yeah. apocalypse kills peter as a punishment for erik's betrayal. jean does her phoenix thing- a little late though babe- and erik loses his son as soon as he finds out he has one ://// does a little pietá reference with how he holds the body, cradling him as he's draped across his lap, as he mourns not only his son but also charles ://///////////////////