When Xorn revealed himself to be Magneto, it was a big show in a run that was meant to be a modern day update of the classic Claremont/Byrne era. Basically, everyone should've saw it coming. There were plenty of hints scattered across the comics leading up to the reveal, but it was a way for Morrison to have Magneto escape the Genoshan Holocaust and attack the X-Men where it counted. During the Planet X storyline, Magneto Xorn tries to reverse the Earth's polarity while creating a Nazi style state in New York City. The special class and the X-Men revolt against him, but he snaps. During Planet X, Xorn is revealed to be a separate personality inside of the drug addicted Magneto. Xorn tries to use Magneto's inner sense of nobility to stop the bloodshed.