Anatole Litvak - Tovarich (1937)

IMDB:
Ousted from their homeland by the Bolshevik revolution, a royal Russian couple find themselves impoverished and living in Paris. They take positions as butler and housemaid in a wealthy household and, owing to their impeccable breeding and manners, excel in their new jobs. But once they are recognized for the royal couple they are, they must face new — and formidable — responsibilities.