If you have not seen the movie and actually plan on watching it, do not read on.
What I cannot comprehend is why did Logan killed Jean at the end. I mean like, haven't they found the "cure" to change mutants into humans?! Just like Magneto, she did not have to die. period.
jean grey had to die be cause she was dark pheonix. in the last scene of the movie where magneto sits in a park, it shows that he slightly moves the metal chess piece with his finger. this shows that the cure’s dna copy injection only lasted temporarily.