Based on what we've heard to far,
Dark Phoenix's third act was reshot to change the location of the climactic battle from outer space to a train. The reason for this change has been debated several times by fans, and addressed unsatisfactorily by the creative team behind the film.
Now, star James McAvoy (Charles Xavier) appears to have shed some more light on the reason for the change.
In an interview with Yahoo UK, the actor addressed the film's reshot third act and what it meant for the finished product:
The end changed a hell of a lot. The finale had to change. There was a lot of overlap and parallels with another superhero movie that came out re—a while ago. And we had no idea that we were...
Michael Fassbender interjected at this point, humorously adding,
"They had spies on set and basically stole our ideas!"
Speculation points to
Captain Marvel being the film with overlap, as the Marvel Studios adventure features the titular heroine engaging in several space-set battles. If
the rumors regarding the Skrulls in
Dark Phoenix prove true, this will only build on this theory, as the alien race is integral in both source material's mythologies.