The Great Lie (1941)

Days after Sandra and Pete elope, they discover their consummated union isn't valid since, unbeknownst to them, Sandra's divorce isn't yet final. They decide to not stay together, but, by then, Sandra is pregnant. She doesn't learn that fact until after Pete marries his former fiancee Maggie. Pete, unaware of the baby, flies to South America on business. While there, a flight he is on goes missing and all onboard are presumed dead. Maggie persuades Sandra to let her adopt the baby, so she can raise it as Pete's legitimate child. Months later Pete - alive after all - returns. Sandra and Maggie contend for him and the baby.