Uncanny X-Men Vol.1 #65
The X-Men make it back to the mansion after their harrowing battle with Magneto only to be commanded inside by Alex and Lorna; They learn that earth is about to be attacked by the alien Z'Nox but a plan has been made to counter the invasion--a plan formulated by none other than the "dead" Professor X; Xavier returns to his charges and explains that Changeling was masquerading as him when he was killed; The X-Men board the Z'Nox space ship and attack but it is the collective power of happy thoughts funneled through Xavier into his students that ultimately drives the aliens off.
Printed: Dec 1977
Writers: Denny O'Neil
Art: Neal Adams and Tom Palmer
Cover: Marie Severin and Tom Palmer