Cactus Flower (1969)

Goldie Hawn won an Oscar for her performance as a Greenwich Village free spirit in Cactus Flower. Middle-aged dentist Winston (Walter Matthau) is enjoying an affair with Toni (Goldie Hawn) but doesn't want to be hemmed in by marriage. He prevails upon his non-glamorous assistant Stephanie (Ingrid Bergman) to pose as his wife so as to keep from campaigning for a ring. Then, to justify his infidelity, Winston talks his pal (Jack Weston) into pretending to be Stephanie's illicit lover. Flattered by all the attention, Stephanie begins to doll up. Confronted by a newly gorgeous Stephanie, Winston realizes that his Dream Girl has been right there in his office all along. As for Toni, she ends up in the arms of a writer (Rick Lenz), who has loved her since Reel One. Cactus Flower was adapted by Billy Wilder's frequent collaborator I.A.L. Diamond from the play by Abe Burrows -- which in turn was adapted from a French farce.