According to Geoffrey of Monmouth, Arthur's full sister and the wife either of King Lot or of King Budic of Brittany.

In a note to 1. 8135 of Chrétien's Perceval, D.D.R. Owen indicates Anna as presumably Ygerne's [Igraine's] daughter and the second of the queens of the Rock of Canguin. [Cline however, in a note to 1. 8135 of her translation, follows Hilka in mentioning Morcads, which is much closer to Morgawse/Margawse, as the name of Arthur's sister and Lot's wife.]