Frühlingsluft (1938)

At the behest of the financially strapped Duke, his nephew, Crown Prince Rudolf, is to marry someone of suitable rank. But Rudolf has no interest whatsoever in his uncle's plans and works under his commoner's name as an engineer in a car factory. Then a certain Count Rasumirski appears before the Duke and explains that the famous operetta diva Vera Naldi is actually a Russian princess who knows nothing of her origins. They hatch a plan to marry Rudolf off to her. But at the theater, Rudolf falls not for the singer, but for the secretary. Instead, Rudolf's other uncle begins to take an interest in Vera. Then, however, it turns out that Rasumirski is an imposter and Vera is not a princess at all...