User blog comment:Krolevnasniezka/Gorlois/@comment-4650675-20120203120031

Morgause may not be Gorlois' child. It's possible that she shared Vivianne as a mother with Morgana and that the father is entirely different to the two sisters. Maybe Uther had the affair with Vivianne before he married Igraine, since he loved her so much and started a war againist magic after losing her. I doubt he would ever have an affair with another woman after Igrayne's death. That's why I think he had Morgana before marrying Igraine. Then he would kill Vivianne and her other daughter, because he simply killed everyone with magic and kept Morgana because she was supposed to be "his best friend's daughter".