Spoilers Incoming for Astonishing X-Men #9 by Charles Soule and Matteo Buffagni, now on-sale. Professor X’s mind may have been freed from the psychic bonds of the Shadow King, but that only gave Proteus a chance to find his way into the vulnerable character’s brain. Xavier came back to life using the body of Fantomex.
Logan remembered the mutant’s healing abilities and slashed away at the Professor’s new vessel, successfully removing Proteus’s control, but not taking into account that his victim doesn’t possess the same regenerative powers as Fantomex. He begins to bleed out and is put to sleep by Psylocke, while Logan utters a funny “oops.”
The grim future that is known as the Mindkiller Apocalypse was mentioned during Astonishing X-Men #7, just when Charles Xavier (now called X) had been resurrected using Fantomex’s body. He had to deal with a massive psychic infection traveling throughout London, spread by the vicious Shadow King.
X removed the infection, and the energy from it formed a giant mass in the sky, which Bishop saw and commented on, calling it a “green sun over London.” Since the character has access to the Endtime Database, he began searching it for any sign of a “green sun” having any negative effect on the future.