Both Complete Peerage, XI, Appendix D, and Eyton, Antiquities of Shropshire vol....
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Both Complete Peerage, XI, Appendix D, and Eyton, Antiquities of Shropshire vol.7, pp. 145, 148, 149, 157, say that Sibil was known by several names! The fact that Reinald had the same mother as Herbert fitz Herbert's children: Reinald called Alice Corbet, the mother of William de Boterell his "matertera" (strict meaning would be maternal aunt, but such terms could be flexible). Benedict of Peterborough says Herbert fitz Herbert was Rainald's brother, and also indicates that he shared a nepos (a younger blood relative) with both Reinald and his brother William, named Joel of Pomeroy (p.163, p.172, p.173). The shared connection to the Pomeroy family must also be through their mother, via Rohese de Pommery, sister of Reinald, who is believed to have married Henri de Pomery. Complete Peeragevol.11 App. D cites a charter of Rainald Earl of Cornwall which calls “Rohesia de Pomeria” his sister, citing the journal of the Royal Institute of Cornwall, vol. i, pp. 29-32). Keats-Rohan, DomesdayDescendants p.642 also cites Bearman's charters of the Redvers family App. II, no. 15a.