In the Annales Cambriae we are told that Arthur and Medrawt (Mordred) perished at Camlan, but we are not told they were on different sides. Geoffrey of Monmouth informs us that Mordred was Arthur’s nephew, the son of Arthur’s sister Anna and her husband, Lot of Lothian. The Dream of Rhonabwy makes him Arthur’s foster-son as well as his nephew. Geoffrey asserts that, when Arthur was away on his Roman campaign, Mordred seized Guinevere and the throne, thus paving the way for their final battle. Ly Myreur des Historires claims Mordred survived the battle, only to be defeated by Lancelot who executed Guinevere – doubtless because he thought she had willingly complied in being seized – and incarcerated Mordred with her dead body which Mordred ate before dying of starvation.

In the earliest Arthurian legends, Mordred seems to have been regarded a hero. It wasn’t until later stories that he becomes a villain.

The incest motif in the story of Mordred’s birth appears only latterly. The earliest occurence is in the Mort Artu. In Malory’s version, Arthur slept with his half-sister Morgause, not knowing they were related and, as a result, Mordred was born. When Arthur discovered the whole truth, in an attempt to kill Mordred he had all children born on the day of Mordred’s birth set adrift. The ship carrying Mordred was wrecked, but he survived and was fostered by Nabur.

As an adult, Mordred became one of Arthur’s knights and was for a time a companion of Lancelot. He took the part of the Orkney family against the family of Pellinore, slaying Pellinore’s son, Lamorak. When Arthur went to fight Lancelot, Mordred was left as regent in his absence. He proclaimed that Arthur was dead and then laid siege to Guinevere, so Arthur’s return became necessary.

In Wace, Mordred is not Arthur’s son, but Guinevere (whom he seized and made his queen) was his sister. In the Alliterative Morte Arthure, he and Guinevere had a child. In Welsh tradition Mordred married Cywyllog, daughter of Caw, and they had two sons. In the earliest Welsh sources he seems to have been regarded as a hero rather than a villain.