You're standing on my neck
After the credits in X3, you see a woman treating some unseen person when that person uses Xavier's voice and says "Hello Moira". Earlier in the movie Xavier had mentioned something along the lines of transferring a person's consciousness. As for how it can still be Patrick Stewart, that wasn't explained but instead brushed aside in the Wolverine after credit scene. When Wolverine asks how it was possible Xavier simply says, "Like I told you long ago, you're not the only one with gifts."
Originally Posted by DisturbedShifty