Uncanny X-Men, Vol. 1 #276 (1991)

Double Death
Gambit and Jubilee attack Xavier, only to lose rapidly. The other X-Men gather quickly, and are told by Gladiator and Xavier that only Deathbird and Lila Chaney were present, not Jubilee and Gambit. Wolverine suddenly attacks Xavier, killing him before Psylocke can subdue him. Battle breaks out, and is ended when Deathbird and Lila return with heavy armaments. They teleport out, leaving Wolverine and Psylocke behind. Deathbird shows the remaining X-Men the devastation that Xavier caused in her name, and applauds Wolverine`s attack. Jubilee is processed as a prisoner. While she doesn`t understand what she sees, it`s clear to experienced Marvel readers that Skrulls have replaced Xavier and Psylocke, and have Lilandra under some level of mental control.
Release Date: 1991