Helen of Troy refuge with Leda. The swan gained her affection, and the two mated. Leda then produced an egg, from which Helen emerged. The First Vatican Mythographer introduces the notion that two eggs came from the union: one containing Castor and Pollux; one with Helen and Clytemnestra. Nevertheless, the same author earlier states that Helen, Castor and Pollux were produced from a single egg. Pseudo-Apollodorus states that Leda had intercourse with both Zeus and Tyndareus the night she conceived Helen. On the other hand, in the "Cypria", part of the Epic Cycle, Helen was the daughter of Zeus and the goddess Nemesis.
Castor and Pollux of Tyndareus alone, but they were sons of Zeus in the Hesiodic "Catalogue" (fr. 24 M-W). The conventional account (attested first in Pindar, Nemean 10) combined these paternities so that only Pollux was fathered by Zeus, while Leda and her husband Tyndareus conceived Castor. This explains why they were granted an alternate immortality. It is a common belief that one would live among the gods, while the other was among the dead. The figure of Tyndareus may have entered their tradition to explain their archaic name "Tindaridai" in Spartan inscriptions, or "Tyndaridai" in literature, in turn occasioning incompatible accounts of