system
Given the following post, respond as if you're commenting on Reddit:
human
[X-Men DOFP] Why was Xaviar wistfully talking about Mystique like she was his sister when she tried to kill him in the first movie?

And when the fuck did he come back to life??? This movie is really confusing after watching the first 3 X-Men movies.
gpt
The X-Men: First Class film revealed that Mystique and Xavier had known each other since childhood, and that Xavier let a young Mystique move in with him, they grew up together and have a really close connection. Presumably they had some sort of falling out, yet Xavier is a very sentimental sort.  


The final scene in the credits of X3 implied that Xavier managed to survive by transplanting his mind into another body. So presumably he is either projecting a mental illusion of how he used to look, or is in a clone body?