On the Riviera (1951)

Jack Martin (Danny Kaye), an American entertainer working cabarets on the French Riviera, does an impersonation of philandering industrialist Henri Duran (Kaye, again) so convincingly that even Duran's beautiful wife (Gene Tierney) is fooled by it.

When Duran's business interests compel him to be in London when he should be hosting a large soiree at his home, Martin is persuaded to impersonate Duran at the party. But matters threaten to get out of hand when Martin (as Duran) is confronted by several of the philanderer's women, and by Duran's ruthless business rival, M. Periton (Jean Murat).