When Zeus saw her, he fell in love with her. He transformed into a swan and appeared in front of her; he seduced her and slept with her. On that night, Leda also lay with her husband. As a result, she became impregnated by both Zeus and Tyndareus. From two eggs, two sets of twins were born; the first set was Helen and Clytemnestra; and the other was Castor and Pollux. In the various myths, it is inconsistent who were the children of Zeus and who were of Tyndareus. All myths agree though that Pollux was immortal, and that Helen was Zeus' daughter. Leda's other children by Tyndareus were Timandra, Phoebe and Philonoe.
Who was Leda?
Leda was a princess in Greek mythology, daughter of the king of Aetolia, Thestius. She was the wife of King Tyndareus of Sparta.