Hercules fell in love with a mortal, Alcmene, despite his marriage with Hera. He disguised himself as Alcmene's husbands and then had an affair with her.
Hera was always jealous of Hercules affairs and this time she would exact her revenge. Knowing that Hercules would be the rightful heir of the throne, she contacted Ilythia, the goddess of childbirth.
Hera knew that another heir, Eurystheus, was to be born soon. She convinced Ilythia to slow down the birth of Hercules and speed up the birth of Eurystheus in order to deny Hercules his birthright.
Hercules was born in the mortal world, but Hera was not done exacting her revenge.
Alcemene was scared of Hera's wrath so she abandoned her son in the wilderness. Athea then saved the child and tricked Hera into caring for him. Hera fed the child her milk making him strong.
Eventually, Hercules was returned to Alcmene. In order to get her revenge, Hera sent two poisonous snakes to kill Hercules. However, due to the added strength he recieved from Hera's milk, Hercules was able to kill the snakes before they could hurt him.