Hebe

"Golden-crowned Hebe," the Goddess of Youth, is a daughter of Zeus and Hera:

Last [Zeus] took blooming Hera for his wife;
Uniting with the king of gods and men,
She bore him Hebe and Ares, and she bore
The goddess Eileithuia to her mate."
-- Hesiod, Theogony (trans. Dorothea Wender)

Despite her parentage, her status on Olympus appears to be that of a servant. She was the cup-bearer, who poured the nectar for the gods, until replaced by Ganymede, a Trojan prince who was abducted by Zeus's eagle. She prepared Ares's bath and harnassed Hera's horses.

"There are no stories about Hebe except that of her marriage to Hercules."
-- Edith Hamilton.

And then strong Heracles, the glorious son
Of trim-ankled Alcmene, at the end
Of all his painful labours, made his bride
Hebe, the modest child of mighty Zeus
And golden-slippered Hera, on snow-clad Olympus."
-- Theogony