Fifty Shades of Grey is coming out next year, but the film's director Sam Taylor-Johnson has been working on the sexy movie for a long time. So, why does she think it's become a huge phenomenon?

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Taylor-Johnson told Harper's Bazaar Sunday that she finds that specific question "difficult to answer."

"I guess I just love the fact that I've never really seen a movie that tackles this subject matter," the director said when asked. "But from the perspective of the millions of other readers, who knows what it is? It's definitely resonated, that's for sure."

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The book on which the film is based by EL James had sold millions of copies and fans can't wait for the movie starring Dakota Johnson (Anastasia Steele) and Jamie Dornan (Christian Grey).

"I think the whole of people's psychology and where they are in life interests me, and the decisions you make that take you on particular journeys to different places," Taylor-Johnson said. "And then Fifty Shades being about a tale of a woman going on this sort of sexual exploration and empowerment-which is the way I see it-that definitely interests me."

Taylor-Johnson lives in London, but has been living in Los Angeles trying to finish the highly-anticipated film. Fifty Shades of Grey is expected to come out on Valentine's Day 2015.

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