"This girl (Grey) is fighting with herself. She really struggles through this movie," explains Turner.

Fassbender, who will appear as the powerful mutant, Magneto, for the fourth time, says the past 10 years has given him opportunities to "explore the character in different stages in his life".

Describing the shooting of the films as "a wonderful journey", Fassbender says the X-Men franchise has also affected his own life. "It has allowed me to set up my own production company and get smaller films made."

McAvoy, who stars as the founder and leader of the X-Men, Professor Charles Xavier, for the fifth time, says the role has always been that of a helpful and positive force in the stories, which will continue in the new film, albeit with a more driven edge.

One of the things that makes Professor X a darker figure this time is that he's more interested in spreading the message of integration between humankind and mutants than just protecting the mutants, says McAvoy.

As of Tuesday, X-Men: Dark Phoenix had topped the presale box office charts for its opening day, accounting for nearly 48 percent of all the takings for Thursday's screenings in China.