Keep an Eye on Amelia (1949)

Young Amélie is currently enjoying life as the kept woman of her reasonably well off boyfriend Étienne. But when Étienne is called off for military duty, he enlists his playboy friend Marcel to keep an eye on her....something of a problem seeing that he is currently looking for a woman with which to create a sham marriage so he can quickly inherit a large sum of money from his father. Then suddenly the Prince of Palestra enters into the picture and boldly asks for Étienne's romantic favors to assess whether or not he would consider taking her as his bride. What's a free-spirited girl to do?