The La Vie en Rose director has just wrapped Grace of Monaco - about the late princess' role in a political spat between France and her adopted home - and he's already under fire for the project.
Prince Albert of Monaco and his sisters released an official statement last week (ends18Jan13), attacking the movie, which read: "For us, this film does not constitute a biographical work but portrays only a part of her life and has been pointlessly glamorized and contains important historical inaccuracies as well as scenes of pure fiction."
And now Dahan is firing back, insisting the film, starring Nicole Kidman and Tim Roth, was never intended as a biopic.
He tells French newspaper Le Journal de Dimanche, "I am not a journalist or historian. I am an artist. I have not made ??a biopic. I hate biopics in general. I have made a human portrait of a modern woman who wants to reconcile her family, her husband, her career, who gives up this career to invent another role.
"Of course there are historical inaccuracies - (French leader) General de Gaulle never set foot at the Red Cross Ball (in Monte Carlo) but I need this stage to tell my story."
Dahan also revealed that the Monaco royals appeared to have changed their tune on the project after working with the director on filming permits in Monaco and discussing script.
He adds, "When I met with the... family... I had the feeling of being listened to."