Complex sentence: It is later revealed that X used the Brig to imprison Professor X, who knew X true nature, he then convinced the other mutants that telepathic powers can't exist and if so they would be very dangerous to them.
Split into simpler sentences: It is later revealed that X used the Brig to imprison Professor X (who knew X's true nature). He then convinced the other mutants that telepathic powers can't exist and if so they would be very dangerous to them.