The Smiling Lieutenant - Ernst Lubitsch

Lieutenant Niki of the Austrian royal guard has a new girlfriend, Franzi. He's crazy about her and is smiling at her while on duty in the street. King Adolf and his daughter Princess Anna from the neighboring kingdom of Flausenthurm drive by, and Anna intercepts a wink meant for Franzi. She falls for Niki, marries him (he has no choice in the matter), and whisks him off to Flausenthurm. Franzi follows and enjoys a brief affair with Niki before Anna finds out. Franzi, much more experienced in the ways of the world, gives Anna lessons on how to win the affections of her husband.