The Man Who Never Was (1966)

American agent Peter Murphy is trying to escape from East Berlin when he encounters his exact double, millionaire playboy Mark Wainwright. After Wainwright is mistaken for him and killed by the KGB, Murphy assumes his identity and lifestyle, which makes a perfect cover for his covert activities. Wainwright's widow, Eva, discovers the deception but plays along, and soon finds herself falling in love with the impostor.