The Livre d’Artus refers to an episode in which Gawain fought Guinganbresil (Guigambresil) at the Castle of the Borderlands. Guinganbresil’s sister had given birth to a son begotten by Gawain. She was distressed that her brother and lover were fighting, so she kept placing herself and her child between them.
In the First Continuation of Chrétien’s Perceval, Gawain fights an identical duel against Brandelis, rather than Guinganbresil, at the Castle of Lis.
Source
Le Livre d’Artus | Early 13th century