Das Schloß in Flandern (1936)

Officers stationed in a castle in Flandes during WWI are comforted by Gloria Delamare's recorded voice. One of them even writes her a letter that will never be sent. When the war is over Miss Delamare takes a tour in Belgium and spends a night in that castle. Most unexpectedly her former admirer appears and they dine and dance together. In the morning he has disappeared and she finds the letter. She tries to find him, only to discover he is presumably dead and involved in a family secret.