Balius and Xanthus

In other traditions, Poseidon is the father of Xanthus along with another horse named Cyllarus to an unnamed mother.

Sarpedon, prince of Lycia and ally of Troy, killed Pedasos when his spear missed Patroclus.

When Xanthus was rebuked by the grieving Achilles for allowing Patroclus to be slain, Hera granted Xanthus human speech allowing the horse to say that a god had killed Patroclus and that a god would soon kill Achilles too.

[1] The horses, named Xanthus and Cyllarus, are the sons of Poseidon, who gave them to Hera as a gift.

The latter bestowed them onto the Dioscuri to use as their horses in battle, and Xanthus retains his ability to speak with Castor.