But now the fourth film in the X-Men prequel series will finally arrive this summer, in what very much looks like a remake of X-Men The Last Stand – but in the new timeline.
Speaking with Entertainment Weekly, director Simon Kinberg revealed why Mystique dies.
He said: “Well, the thought process behind that was to primarily show that this is a movie that is unlike other X-Men movies.
“It’s a movie where shocking things happen, where intense, dramatic things happen.”
He added: “People don’t just fall off buildings and dust themselves off and walk away.
“There’s a reality to this movie and a consequence to this movie.
“Even more than that, it was to show that Jean/Dark Phoenix is genuinely a threat to everyone, including the X-Men.”
The official synopsis reads: “In DARK PHOENIX, the X-MEN face their most formidable and powerful foe: one of their own, Jean Grey.”
The synopsis continues: “During a rescue mission in space, Jean is nearly killed when she is hit by a mysterious cosmic force. Once she returns home, this force not only makes her infinitely more powerful, but far more unstable.
“Wrestling with this entity inside her, Jean unleashes her powers in ways she can neither comprehend nor contain. With Jean spiralling out of control, and hurting the ones she loves most, she begins to unravel the very fabric that holds the X-Men together.
“Now, with this family falling apart, they must find a way to unite – not only to save Jean’s soul, but to save our very planet from aliens who wish to weaponize this force and rule the galaxy.”
Dark Phoenix is released in UK cinemas on June 7, 2019.