Gratian

The Western Roman Emperor Gratian was expected to help his uncle Valens, Augustus in the East, at the Battle of Adrianople. Valens, possibly distrusting his nephew, and certainly disagreeing with him on religious grounds, may have deliberately entered the fray knowing his nephew couldn't make it in time to help. Presumably Valens thought he would win and take the glory, but he died, and Gratian had to appoint a new emperor in his place.
Gratian