X-Men: The Last Stand
Professor Xavier tracks down Jean Grey.  He and Wolverine and Storm go Jean's old house to try to talk to her.  Early on, he found that Jean Grey had a very powerful side called the Phoenix.  To make sure that side never came out, he put up a mind barrier.  During the talk, the Phoenix comes out and he and Jean Grey have a mind battle.  It ends when the Phoenix overpowers the Professor and the Professor dies.