 It relates that Guinevere, described as one of the great beauties of Britain, was descended from a noble Roman family on her mother's side and educated under Cador, Duke of Cornwall.Arthur leaves her in the care of his nephew Modredus (Mordred) when he crosses over to Europe to go to war with the Roman leader Lucius Tiberius.While her husband is absent, Guinevere is seduced by Modredus and marries him, and Modredus declares himself king and takes Arthur's throne.