The Moderns (1988)

Keith Carradine plays the artist Nick Hart

The Moderns on IMDB

Nick Hart is an expatriate American fictional artist living in Paris among some of the great artists and writers of the time, including Ernest Hemingway, Gertrude Stein, and Alice B. Toklas.

Nick is torn between his wife Rachel and Nathalie de Ville who hires him to forge her paintings. He must also contend with Rachel's current husband, Bertram Stone, who does not know that his wife is still married to another man.