Book II - Chapter IV - How Merlin told the adventure of this damosel.
AT that time there was a knight, the which was the king's son of Ireland, and his name was Lanceor, the which was an orgulous knight, and counted himself one of the best of the court; and he had great despite at Balin for the achieving of the sword, that any should be accounted more hardy, or more of prowess; and he asked King Arthur if he would give him leave to ride after Balin and to revenge the despite that he had done. Do your best, said Arthur, I am right wroth with Balin; I would he were quit of the despite that he hath done to me and to my court. Then this Lanceor went to his hostelry to make him ready. In the meanwhile came Merlin unto the court of King Arthur, and there was told him the adventure of the sword, and the death of the Lady of the Lake. Now shall I say you, said Merlin; this same damosel that here standeth, that brought the sword unto your court, I shall tell you the cause of her coming: she was the falsest damosel that liveth. Say not so, said they. She hath a brother, a passing good knight of prowess and a full true man; and this damosel loved another knight that held her to paramour, and this good knight her brother met with the knight that held her to paramour, and slew him by force of his hands. When this false damosel understood this, she went to the Lady Lile of Avelion, and besought her of help, to be avenged on her own brother.