Agravain

Sir Agravain or Sir Agravaine is a nephew of King Arthur and a Knight of the Round Table in Arthurian legend. He is the second son of King Lot of Orkney and Lothian and Morgause; his brothers are Gawain, Gaheris, Gareth, and Mordred. His mother's parents were Gorlois and Igraine; she was a sister of Elaine and Morgan le Fay and maternal half-sister to King Arthur.
See more at Wikipedia.org...

[Arthurian] Son of Lot and Morgause and brother to Gawain both in Malory and the Vulgate Cycle. He plays a leading role in exposing the infidelity of Guinevere and Lancelot, supported by Mordred. He is slain by Lancelot.