Le secret des Woronzeff(1935)

Gravely ill, Prince Woronzeff asks a friend and look-alike, Franz von Naydeck, to replace him at the wedding of his daughter Nadia, whom he has just found, as the family covets the inheritance. Diane, who once loved the prince, doesn't betray the secret, because she now loves Franz and separates him from his pseudo-daughter, with whom he had begun to fall in love.