James, who wrote the bestselling erotic novels on which the franchise is based, had the final say on the film's outcome, meaning many of Marcel's script ideas were eventually rejected.
"My heart really was broken by that process, I really mean it," Marcel said on Bret Easton Ellis' podcast. "I don't say it out of any kind of bitterness or anger or anything like that. I just don't feel like I can watch it without feeling some pain about how different it is to what I initially wrote."
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Marcel wanted the screenplay to take a non-linear approach to James' story about BDSM-loving billionaire Christian Grey and his submissive Anastasia Steele, but was repeatedly overruled.
"I wanted to begin at the end of the film and for us to meet in the middle, so you start with the spanking and you have these sort of flashes that go throughout the film," she said.
"I wanted to take the inner goddess out and all of Ana's inner monologue. I felt it could be a really sexy film if there wasn't so much talking."
But although Marcel's "crazy and artistic" vision received a warm reaction initially, she soon realised that James "had all of the control".
"Erika was like, 'This isn't what I want it to be and I don't think this is the film the fans are looking for'," she said.
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Reports prior to Fifty Shades of Grey's release alleged that James removed all edits until the script was to her liking, even after award-winning playwright Patrick Marber was hired to hone Marcel's attempt. Marber has not seen the movie either.
Marcel has also quit the franchise, with James' screenwriter husband Niall Leonard on board to pen the next film. Rumours suggest that James wants to write the script herself, but this is yet to be confirmed.
Lead stars Jamie Dornan and Dakota Johnson are believed to be returning for Fifty Shades Darker, reportedly on much higher salaries. Fifty Shades of Grey proved a box office smash, grossing $569.6 million worldwide despite poor reviews from critics.
Universal is yet to find a replacement director. James' representatives have been approached for comment on Marcel's remarks but did not immediately respond.
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