Britain's Royal Families: The Complete Genealogy, rev. ed. @ p 68, d of Richard FitzGilbert de Clare, 2nd E of Pembroke, no mother, no title
The cited information was published by Pimlico Random House, London, England, 1989, 1996 (Ref: p 68, d of Richard FitzGilbert de Clare, 2nd E of Pembroke, no mother, no title) The author/originator was Alison Weir.