The Ecclesiastical History of Socrates Scholasticus 45The Death of Constantine the Younger.

Not long after this the brother of the Emperor Constantius, Constantine the younger, who bore his father's name, having invaded those parts of the empire which were under the government of his younger brother Constans, engaging in a conflict with his brother's soldiery, was slain by them. This took place under the consulship of Acindynus and Proclus.