The prince and his sisters, Princess Caroline and Princess Stephanie, said "numerous requests for changes" had been ignored and that the latest screenplay "had caused much astonishment".
In a statement, the royal House of Grimaldi described a "series of scenes" in the forthcoming film Grace of Monaco, starring Nicole Kidman and directed by Olivier Dahan, as "purely fictional". "Therefore, the royal family wishes to stress that this film in no way constitutes a biopic," it said. "It recounts one rewritten and needlessly glamorised page in the history of Monaco and its family with both major historical inaccuracies and a series of purely fictional scenes."
American-born Kelly was one of the world's most famous film stars when she married Rainier III Prince of Monaco, Albert's father in 1956, becoming Princess Grace of Monaco. She died in a car crash in 1982 at the age of 52.
In a recent interview, Kidman said, "This is not a biopic or a fictionalised documentary of Grace Kelly but only a small part of her life where she reveals her great humanity as well as her fears and weaknesses."