Britain's Royal Families: The Complete Genealogy, rev. ed. @ p 48, Sybilla, AKA Adela or Lucy, d of Sir Robert Corbet
The cited information was published by Pimlico Random House, London, England, 1989, 1996 (Ref: p 48, Sybilla, AKA Adela or Lucy, d of Sir Robert Corbet) The author/originator was Alison Weir.