Excerpts from Books and Wikipedia
"Fourteen-year-old Constans, despite his age, soon showed that he was not to be trifled with. In 340, his brother Constantine II tried to take Italy from him; Constans went to war against his older brother, ambushed him in the north of Italy, and killed him. Now the empire was again divided into two, between Constans in the west and Constantius in the east. Constans was a staunch supporter of the Christian church; nevertheless, he was unpopular with everyone. His personality was so foul that even the church historians, normally fulsome about any Christian emperor, disliked him. He managed to survive for another ten years, but in 350, at age twenty-seven, he was murdered by his own generals. Rather than throwing their support behind the remaining brother, Constantius, the generals then acclaimed a new co-emperor: an officer named Magnentius. Constantius marched west to get rid of the usurper, but it took two years of fighting before Magnentius was defeated. He killed himself rather than fall into Constantius’s hands. By 352, Constantius (like his father) was ruler of the entire empire." [Bauer: Medieval World, p. 32-3]