Her Mother's Secret (1915)

Seth Cartwright abandons his mistress Bernice Archer and their child, Lorna returning to his wife and son. Bernice, in a daze, leaves Lorna, who is adopted by Cartwrght's wife, who knows full well who the child's father is. Unfortunately, she and her husband are killed in a shipwreck, but it turns out Lorna and her real mother are reunited because of the wreck, and settle in a small seaside town. Matters get complicated when Seth Jr. arrives in the town for a vacation and falls in love with Lorna--not knowing that she is his half-sister.