Morgana

In Arthurian legend Morgana or Morgan le Fey is often the half-sister of Arthur having been the offspring of Gorlois, Duke of Cornwall and Igraine, Arthur's mother.

The name Morgana or Morganna stems from Ambrosius' semi-mytholgical, half-sister, Anna.

TH White
Find out about the famous Arthurian fantasy

Bernard Cornwell
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Marion Zimmer Bradley
Find out about her best selling Arthurian novel