Page "Alcmene" Paragraph 4

In Homer's Iliad, when Alcmene was about to give birth to Heracles, Zeus announced to all the gods that on that day a child, descended from Zeus himself, would be born who would rule all those around him.

Hera, after requesting Zeus to swear an oath to that effect, descended from Olympus to Argos and made the wife of Sthenelus ( a son of Perseus ) give birth to Eurystheus after only seven months, while at the same time preventing Alcmene from delivering Heracles.

This resulted in the fulfilment of Zeus's oath by Eurystheus rather than Heracles.