Indiscreet (1958)

Cary Grant is the suave American diplomat who pretends to be married in order to preserve his bachelor status. Ingrid Bergman is the glamorous leading lady of the London stage who has no scruples about having an affair with a married man. Soon their blazing romance is the talk of the town, but when Bergman discovers that Grant is not married, sparks really begin to fly. Based on Norman Krasna's play, "Kind Sir."