Flavia Maxima Constantia

Flavia Maxima Constantia was the first Empress consort of Gratian of the Western Roman Empire. According to Ammianus Marcellinus, Constantia was a posthumous child of Constantius II by his third wife Faustina. Her paternal grandparents were Constantine the Great and Fausta.

OnOctober 361, Constantius II died of a fever at Mopsucrenae, near Tarsus, Cilicia. He was heading west to face a revolt by Julian, his first cousin and brotherinlaw. In a reported deathbed decision, Constantius officially acknowledged Julian as his heir. When Constantia was born sometime after, Julian was already firmly established on the throne.

Source: Wikipedia