Hi RJ
1. "Royal Ancestry" D. Richardson, 2013, Vol. I. p. 418.
* D. Richardson's RA ... Eleanor De Bohun, married Robert De Ferrers, Knt., 6th Earl of Derby
2. "Royal Ancestry" D. Richardson, 2013, Vol. II. p. 565.
* Robert De Ferrers, Knt., 6th Earl of Derby, son and heir by his father's 2nd marriage, born about 1239. He married (1st) Mary (or Marie) De Lusignan (or Mary De La Marche, daughter of Huges XI le Brun (or de Lusignan), Knt., Count of La Marche and Angouleme, seigneur of Lusignan in Poitou (uterine half-brother of Henry III, King of England, by Yolande, daughter of Pierre de Braine, Knt., Duke of Brittany, Earl of Richmond.
Thank you!