Britain's Royal Families: The Complete Genealogy, rev. ed. @ p 67, Peter Mauclerk, Count of Brittany, no parents
The cited information was published by Pimlico Random House, London, England, 1989, 1996 (Ref: p 67, Peter Mauclerk, Count of Brittany, no parents) The author/originator was Alison Weir.