Fred Astaire's Widow Sends Threatening Legal Letter to Sony Biopic Producers

2:25 PM PT -- A source with direct knowledge of the production tells TMZ … the film is based on a book, which Sony owns the rights to.

Tom Holland's set to star in an upcoming biopic about Fred Astaire ... but the late Hollywood legend's widow says the movie never got the green light from Fred's estate.

TMZ obtained a legal letter Fred's widow, Robyn Astaire, fired off to Amy Pascal -- one of the biopic's producers -- and Robyn makes it clear she hasn't authorized or granted permission for any portrayal of Fred in this biopic ... or any other film.

In the letter, Robyn says Fred "was explicit in his Will that he did not want his life story to be depicted on screen" ... and he says she "fully respects and upholds those wishes."

Robyn says no biopic has been approved or endorsed by Fred's estate ... and she says if producers move forward with a movie that goes against Fred's wishes, they should be careful about misrepresenting her involvement.

Fred's widow threatens legal action if producers claim she authorized the biopic.

The biopic has been in development since 2021, when it was first announced as a Sony project ... and Tom's confirmed he's playing Fred.