Days of Future Past How Was Xavier Alive?

[Jedi Arrow]

Hi, all! I watched DOFP for the first time this weeken, and I was wondering, how was Xavier alive after the events of X3? I know how Magneto had his powers back, but last I knew, Xavier had died at Phoenix's hands. How is he alive and well in the future scenes in DOFP?

 

[Herofan]

The real reason is Singer, Kinberg, the producers didn't care about continuity and especially about X3.

But I believe the in-universe explanation is that Xavier, at the last minute, somehow transferred his consciousness to a comatose or brain-dead twin of his.