Her paternal grandparents were John of Brienne, King of Jerusalem, Emperor of Constantinople, and Berenguela of Leon, and her maternal grandparents were Geoffrey VI, Viscount de Chateaudun and Clémence des Roches.
Blanche had a uterine half-sister Beatrice de Montfort, Countess of Montfort-l'Amaury from her mother's first marriage to Jean I de Montfort (died 1249 in Cyprus).
[2] His other titles included Lord of Wendover, Buckinghamshire, of Lambourne, Essex, of Chokes and Gayton, Northamptonshire, of Martock, Somerset, of Carshalton and Clapham, Surrey, and custodian of the county of Ponthieu.
[3] William and Blanche had at least one son and two daughters: She married William de la Planche (1240–1302) and had at least one son: In 1285, Blanche received the gift of twelve leafless oak stumps from Selwood Forest from King Edward I for her fuel.
[3] Blanche de Brienne died on an unknown date around the year 1302.