Sophie Turner "gobbled up" her research into mental illness as preparation for her role in Dark Phoenix.

In the latest X-Men franchise film, Turner's character Jean Grey gets hit by a cosmic force in space and starts to lose her mind. To help his leading lady get into character, the film's director, Simon Kinberg, bombarded her with materials on mental illness for nine months.

"I sat down with her and I said, 'Look. This is the story. You know it from the comics. I need you to fully inhabit this sense of losing control, losing your sanity. I need it to feel real...'," Kinberg tells Us Weekly magazine.

"I sent her books, articles and videos about people suffering from schizophrenia, dissociative identity disorder, multiple personality disorder...," he continues. "She gobbled it up. She would read and send me back things as fast as I could send her... She was walking around the streets of London and New York with earphones in her ears listening just to random voices, so that she knew what it would be like to walk around with too many voices in your head and be overloaded, or to lose your mind and really experience what it is, as close as possible, to being schizophrenic."

Turner's dedication to the role paid off and the former Game of Thrones star's performance really impressed her fellow A-listers.

"Michael Fassbender, Jennifer Lawrence, James McAvoy, Jessica Chastain - there's a lot of Academy Award nominations and wins in that group, and she (Sophie) not only held her own, but kicked some a** in those scenes," Kinberg adds.

"So much so that every single time one of those actors was acting across from Sophie for the first time, after the first take they would come up to me and they would say, 'Jesus Christ. She is unbelievable.' Every single one of them."