Pendragon
Bearing the same name as Uther Pendragon, this sounds as if it should have been a more important castle than Malory otherwise seems to indicate.
The lord of Pendragon Castle at the time of Sir La Cote Male Taile was Sir Brian de les Isles,
a noble man and a great enemy unto King Arthur.
Lancelot vanquished him and freed from his castle thirty of Arthur’s knights, including La Cote Male Taile (Brunor the Black), and forty ladies. Lancelot made La Cote Male Taile lord of Pendragon, following his marriage to Maledisant, with Sir Nerovens de Lile his lieutenant to have rule of the castle under him.
La Cote Male Taile came to Pendragon after leaving Castle Orgulous, for which I incline to accept Glennie’s identification of Bamborough (Bamburgh).
See also
Neroneus of the Isle | The Legend of King Arthur
Source
Le Morte Darthur | Sir Thomas Malory, 1469-1470