Guillaume de Gisors
Guillaume de Gisors (1219-1307). Son of Hugues III de Gisors and grandson of Jean de Gisors. He was supposedly the third grand master of the Priory of Sion.
According to the genealogies in the "Prieuré" documents his sister married one Jean des Plantard. They also state that Guillaume was inducted into the Order of the Ship and the Double Crescent in 1269. This order was created by Louis IX (Saint-Louis) for nobles who accompanied him on the ill-fated Sixth Crusade.