Cousin of King Lancelot de la Blance Terre. The duke was married to King Lancelot’s mistress.
When Lancelot de la Blance Terre was drinking from a chapel fountain, the Duke of the White Fortress, sneaked up behind him and beheaded him. Lancelot’s head landed in the fountain which started to boil, burning the Duke. The fountain continued to boil until the Grail Quest, when Galahad put his hand into the fountain. Lancelot of the Lake found his grandfather’s body and buried it next to his grandmother’s.