The Smiling Lieutenant (Paramount Pictures, 1931) is an American film directed by Ernst Lubitsch, starring Maurice Chevalier and Claudette Colbert. Made in the Pre-Code era, it was written by Samson Raphaelson and Ernest Vajda, from the operetta Ein Walzertraum by Oscar Straus (libretto by Leopold Jacobson and Felix Dörmann), which in turn was based on the novel Nur der Prinzgemahl (Only the Prince Consort) by Hans Müller-Einigen. The film was directed by Ernst Lubitsch and was nominated for the Academy Award for Best Picture.
The story is a romantic comedy concerning the love of a Princess for a soldier, and the love of the soldier for another woman. The Lieutenant Nikolaus 'Niki' von Preyn (Maurice Chevalier) while standing in formation before a parade honoring the visiting royal family of Flausenthurm takes an opportunity to smile at his girlfriend Franzi (Claudette Colbert) in the crowd. Unfortunately the smile is intercepted by Princess Anna of Flausenthurm (Miriam Hopkins), and an international incident is narrowly avoided by having the lieutenant and princess marry.
Nikolaus sneaks away from his bride to wander the streets of Flausenthurm and there discovers Franzi. The Princess Anna hears of this and decides to confront Franzi. After this meeting, Franzi sees that the princess is in fact deeply in love with Nikolaus, and decides to save the marriage by giving the princess a makeover ("Jazz up your lingerie!") The results are a complete success as the lieutenant follows his satin-clad, cigarette-puffing bride into the bedroom and closes the door — only to open it and give the audience a last song and a suggestive wink. -- adapted from Wikipedia