In a statement, Prince Albert II and Princesses Caroline and Stephanie said the film was completely fictional and did not accurately portray events involving their mother, the Hollywood actress who married Monaco's Prince Rainier III in 1956.

"Grace of Monaco", directed by France's Olivier Dahan, will officially open the 67th Cannes festival on May 14 when it will be simultaneously released in France and several cities around the world.

But even before its release, the film has been mired in controversy, with Dahan locked in a standoff with the film's US producer Harvey Weinstein and the Monaco royals slamming it as pure fantasy.

"The Prince's Palace would like to reiterate that this feature film cannot under any circumstances be classified as a biopic," the Monaco royals said Friday.