Morgan was the half-sister of King Arthur and mother of Mordred.
A year after the Tremas Master had arrived in Camelot and become Arthur's new Merlin, Morgan gave birth to Mordred in Lothian. When he heard about this, Arthur sent the Master to kill Mordred. The Master allied with Morgan to help raise Mordred so when he grew up he could kill Arthur at the battle of Camlan. This would result in Britain never becoming one country. The Master fooled Arthur into thinking Morgan and the Master were enemies and that Mordred was dead. (PROSE: The Creation of Camelot)