She was to be the prize of a tournament at the Castel de la Marche, held for the purpose of getting her a good husband. Sir Bors won the tournament, but, having sworn to remain chaste all his life, cried off by pleading that he was not ready to take a wife until his current quest – to avenge King Agrippe’s daugter – was done.
Brandegoris’ daughter fancied Bors. With the connivance of her old nurse, who gave Bors a ring to make him love the princess, the damsel spent the night with Bors, and Sir Helin le Blank was the result. The spell was broken in the morning when the ring fell off.
The twelve best knights of this tournament, after Bors, gave the princess “gifts” of varying silliness of bloodthirstiness. One, for instance, promised to cut off the heads of all the knights he conquered and send them to the princess.
The details given above come from Vulgate IV, but the princess is mentioned three or four times by Malory, once as the daughter of King Brandegore and always as the mother of Helin le Blank.
Brandegorre | The Legend of King Arthur
Vulgate Lancelot | 1215-1230
Vulgate Merlin | 1220-1235
Le Morte Darthur | Sir Thomas Malory, 1469-1470