Take Two (1988)

"Twin brothers...One's her husband, one's her lover. One's a murderer."

A dying woman tells her son, Barry Griffith, she had been a surrogate mother for a millionaire, and that he is a twin to that baby. He seeks out his twin, Frank Bentley to get a bite of his inheritance, but he's not the first long-lost brother to call. Barry stakes out across the street from Frank's home so he can spy and release the story to a tabloid paper. In the process, he begins an affair with Frank's mistreated wife.