Britain's Royal Families: The Complete Genealogy @ p 68
The cited information was published by rev. ed, Pimlico Random House, London 1989, 1996 (Ref: p 68) The author/originator was Alison Weir.
References (3)
Parent Source:
Britain's Royal Families: The Complete Genealogy
Family:
Gilbert De Clare & Isabelle Marshall
Individual:
Richard De Clare