Vivienne

Vivienne was the wife of Gorlois and the mother of Morgana Pendragon and Morgause.

Biography
When she was young - or at least, before Morgana was born - Vivienne was a lady-in-waiting to Ygraine Pendragon. Morgause was then a young child, or at least old enough to remember Ygraine. When Gorlois was away on the Northern Plains, Vivienne had a brief affair with Uther Pendragon, which roughly nine months later resulted in the birth of Morgana. She had Gorlois believe that he was the father of her second child and it is likely that he never found out about his wife's affair. Vivienne was a witch, or at least, had magical powers, and passed on her magical powers to her two daughters. She possessed a healing bracelet that was forged on the Isle of the Blessed, which she gave to the young Morgause when she was smuggled from Camelot by Gaius. Morgause later passed the bracelet on to her younger half-sister, Morgana, who was roughly nine months younger than her, as Morgana remembered that she had met Morgause at least once before Morgause was taken from Camelot.

Gaius was asked to smuggle Morgause out of Camelot after she was born. He gave her to the High Priestesses of the Old Religion but it is unknown why and if this is what Vivienne requested. Nevertheless, due to an unknown reason, Uther was led to believe that Morgause had died shortly after her birth and only discovered the truth approximately twenty eight years later when Morgana returned to Camelot.

It remains unknown what happened to Vivienne after Morgana's birth. As Morgana has spoken only of Gorlois and has not referred to her mother, Vivienne may have died before her husband. However, it is unknown if Uther included Vivienne in his purge of magic that he started several years later when Arthur was born. It is possible that Vivienne is still alive and either went into hiding or left Camelot after Gorlois died.

Trivia

 * So far it is unknown what happened to Morgana’s mother but there is the potential to see her ally with her daughter and return to Camelot - as well as the threat of Merlin falling under the spell of an older woman.
 * King Mark is also sometimes credited as the one who sends the passionate and evil witch, Vivienne, to Arthur’s court to undermine his influence. Vivienne spreads vicious rumours about Arthur, teasing and seducing Merlin - leading to his disappearance from Camelot (often she’s said to entrap Merlin in a cave or tree). http://www.cultbox.co.uk/features/opinion/3545-merlin-four-legendary-characters-wed-like-to-see-in-series-5

In the Legend
Vivienne, spelled Viviene, is one of the names for the Lady of the Lake. Also known as Nimueh or Ninane, she is the one who gives Excalibur to Arthur, steals the infant Lancelot and traps Merlin in a tree.