The Pageant of England The Magnificent Century @ Younger brother of William de Burgh. Believed to be descended
from Robert de Mortain, a 1/2 brother of the Conqueror.
The cited information was published by Doubleday & Company, Garden City, NY, 1951 (Ref: Younger brother of William de Burgh. Believed to be descended
from Robert de Mortain, a 1/2 brother of the Conqueror.) The author/originator was Thomas B. Costain.