One can’t help thinking that Leda knew more than she was telling. Legendarily one of the most beautiful women in ancient Greece, this queen of Sparta dallied with a swan (who, it turned out, was actually Zeus in disguise), and gave birth to perhaps the only woman to be more beautiful than her: Helen (later of Troy).
In fact, she gave birth to four children, two sets of twins. Half of them were mortal, the children of Tyndareus (her human husband), and half were half-divine, the children of Zeus. Which children are descended from which father is inconsistent across the various tellings of the myth, although a majority of versions record that Helen was half-divine (accounting for her legendary beauty).