In some of the romances there is great confusion between Elain (the sister) and Morgause (the half-sister) of Arthur.  Both are called the mother of Mordred, and both are also called the wife of Lot.  This, however, is a mistake.  Elain was the wife of sir Nentres, and Morgause of Lot; and if Gawain, Agrawain, Gareth, and Gaheris were [half-]brothers of Mordred, as we are told over and over again, then Morgause and not Elain was his mother.  Tennyson makes Bellicent the wife of Lot, but this is not in accordance with any of the legends collected by sir T. Malory... (Character Sketches of Romance, Fiction and Drama, Brewer, 1902)