Herzkönig (1947)

After drinking too much alcohol, King Michael XXXVII promptly forgets his own wedding date! To avoid a scandal, his police minister asks the writer Peter Petroni, who looks deceptively like the king, to stand in for the alcoholic Michael at the ceremony. The only trouble is that the game quickly turns serious - because when Peter catches sight of "his" bride at the altar, it's love at first sight...