After the death of his father in 38, Mithridates III became joint-ruler with his mother Gepaepyris, and sometime between 38 and 45, Roman Emperor Claudius made him ruler of all of the Bosporan Kingdom.

At the same time, Claudius withdrew the Roman garrison under Aulus Didius Gallus leaving only a few cohorts under Gaius Julius Aquila.

When Cotys heard of this, he turned to Gaius Julius Aquila and his Roman cohorts to help him fight off his elder brother.

Cotys and Aquila feared that Mithridates's army was larger, and enlisted the help of Eunones, who was at the time ruler of the Aorsi.

This act of greatly affected Eunones, and he raised the former ruler and was pleased that Mithridates had chosen the Aorsi to help him sue for mercy with Rome.