Writer Kelly Marcel will never watch 'Fifty Shades of Grey' because the changes author E.L James made to her script left her heartbroken.

The 41-year-old screenwriter and actress has confessed she refused to see the film - which was based on James' novel of the same name - after the pair clashed while penning the script.

Kelly insists seeing the film - which was released in February and stars Dakota Johnson and Jamie Dornan - would be too painful as it is ''much different'' to the one she had originally imagined.

She explained: ''My heart really was broken by that process, I really mean it. I don't see 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.''

Marcel also opened up about the strained relationship between James and director Sam Taylor-Johnson, who has dropped out of the next installment of the racy franchise.

She told Vulture: ''There was a moment where we were weeks away from shooting ... and it was clear that that was gonna be a struggle.

''It's very difficult to come on as a director and to be handcuffed that way and not be able to fulfil your creative vision because there are certain restrictions on you. But at the same time, I would argue that it was very clear that that was the way it was going to be.

''She would always let me argue and fight for things that I felt passionate about. In the end, I think we ended up with a draft that was a halfway compromise, but she had still been very brave about what she had let go. Ultimately, Erika did have all of the control.''