Royal Flash (1975)

Captain Harry Flashman (Malcolm McDowell) of the British Army is a cad, a coward, and a lecher who always seems to come off inadvertently heroic. While romancing renowned courtesan Lola Montez (Florinda Bolkan), Harry is recruited against his will by Otto Von Bismarck (Oliver Reed) to substitute for a lookalike Prussian Prince ostensibly in order to help Bismarck enlarge his hold over German duchies. But Bismarck has something more sinister in mind for Harry and the Prince.