Bellangere le Beuse, Bellangre the Bewse, Bellangere of Magouns, Bellangerus
Son of Alisander Le Orphelin and Alice La Beale Pilgrim. Bellangere avenged the death of his father and his grandfather, Prince Boudwin, by killing King Mark of Cornwall.
And by Alice he [Alisander] gat ... Bellengerus le Beuse. And by good fortune he came to the court of King Arthur, and proved a passing good knight; and he revenged his father's death [apparently by killing King Mark].
Bellengerus became a knight of the Round Table, being listed in Malory XIX, 11. When Sir Lancelot and Queen Guinevere were accused of treason, Sir Bellangere pledged his support to Lancelot and helped him rescue Guinevere from the stake. He fought alongside Lancelot when Arthur laid siege to Joyous Guard and, later, Benoic (Benwick). In return for his support, Lancelot made him the Earl of the Laundes.
Very likely he was named for Sir Belangere, the constable of Magouns Castle, who had taken in Bellengerus’ grandmother, Anglides, when she fled from King Mark.
Source
Le Morte Darthur | Sir Thomas Malory, 1469-1470