Who is Helena from Julian and what is their importance?

Helena was Julian's wife and Constantius' sister. It is believed that Helena was married off to Julian, so that Constantius could keep an eye on him. In the end, it is Helena who urges her husband to become Augustus. Much older than her husband, the couple had no children..... unfortunately for Constantius, Helena knew that it was Constantius' wife Eusebia who paid the midwife to end the life of their only child.