Keroessa

Keroessa (Ancient Greek: Κερόεσσα) was a demigod daughter of Zeus and Io from Greek mythology. She was the mother of Byzas by Poseidon.

Mythology
Io gave birth to Keroessa while she was still transformed into a white cow. Keroessa was born near the altar of the nymph Semestra, so she was raised by the nymph. Keroessa was an incredibly beautiful woman and ended up having an affair with Poseidon.