New X-Men Vol. 3: New Worlds
Grant Morrison (Writer); Ethan Van Sciver, Igor Kordey, Phil Jimenez, and John Paul Leon (Artists)
His name is Charles Xavier...and he is a mutant. For years, Professor X was widely regarded as an authority on genetic mutation, and an advocate of peaceful relations between man and mutant. The general public was unaware he possessed superhuman powers until the psionically empowered psychopath Cassandra Nova -- his twin sister -- addressed the global media while in possession of her brother's body and broke his decades-long silence. But in attempting to expose Xavier to his enemies, she unwittingly freed him from his self-imposed exile.
New X-Men (1st series) #127-133