Mordred (Sir), son of Margawse (sister of king Arthur) and Arthur her brother, while she was the wife of Lot king of Orkney (pt. i. 2, 35, 36).  The sons of Lot himself and his wife were Gawain.  Agravain, Gaheris, and Gareth, all knights of the Round Table.  Out of hatred to sir Launcelot, Mordred and Agravain accuse him to the king of too great familiarity with queen Guenever, and induce the king to spend a day in hunting.  During his absence, the queen sends for sir Launcelot to her private chamber, and Mordred and Agravain, with twelve other knights, putting the worst construction on the interview, clamorously assail the chamber, and call on sir Launcelot to come out.  This he does, and kills Agravain with the twelve knights, but Mordred makes his escape and tells the king, who orders the queen to be burnt alive.  She is brought to the stake, but is rescued by sir Launcelot, who carries her off to Joyous Guard, near Carlisle, which the king besieges.  While lying before the castle, king Arthur receives a bull from the pope, commanding him to take back his queen.  This he does, but as he refuses to be reconciled to sir Launcelot, the knight betakes himself to Benwick, in Brittany.  The king lays siege to Benwick, and during his absence leaves Mordred regent.  Mordred usurps the crown, and tries, but in vain, to induce the queen to marry him.  When the king hears thereof, he raises the siege of Benwick, and returns to England.  He defeats Mordred at Doveer and at Barondown, but at Salisbury (Camlan) Mordred is slain fighting with the king, and Arthur receives his death-wound.  The queen then retires to a convent at Almesbury, is visited by sir Launcelot, declines to marry him, and dies.—Sir T. Malory: History of Prince Arthur, iii. 143-174 (1470).
    N.B.—The wife of Lot is called "Anne" by Geoffrey of Monmouth (British History, viii. 20, 21); and "Bellicent" by Tennyson, in Gareth and Lynette. 
    (This tale is so very different to those of Geoffrey of Monmouth and Tennyson, that all three are given.  See Modred, p. 714.) (The Reader's Handbook of Famous Names in Fiction, &c., Brewer, 1899)