Commentary
Cawley: "The sources which report the parentage of the wife of Gilbert de Lacy are conflicting. A manuscript which narrates the descents of the founders of Lanthony Abbey records that “Gilbertus de Lacy” married “Isabellæ Mareschal”, presumably confusing her with Isabel daughter of William Marshal Earl of Pembroke who married firstly Gilbert de Clare Earl of Gloucester and Hereford and secondly Richard Earl of Cornwall. The Chronicle of Tintern Abbey, Monmouthshire names "Isabella soror Johannis" as daughter of ”Rogerus sive Radulphus Bigod, secundus filius Hugonis le Bigod com. Norfolke et Suffolke…” and his wife “Bertam de Fornivale”, adding that she married firstly "Gilberto de Lacy" and secondly "Johanni Fitz-Geffrey". This must also be incorrect, as any children of Ralph Bigod could not have been born before the late 1220s at the earliest, which is inconsistent with the timing of Isabel’s first marriage. If Isabel was a member of the Bigod family, she must have been the daughter of Hugh and Matilda Marshal of Pembroke. This is the solution adopted by the Complete Peerage, although the primary source on which this is based has not been identified. "
Family
ClaimDetailEvidence
FatherHugh Bigod, 3rd Earl of Norfolk (e1178-1225) [S756] [S954]
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MotherMatilda Marshal (e1190-1248) [S756] [S954]
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Spouse 2ndSir John fitz Geoffrey, Lord of Hallamshire (e1207-1258) 
Child +Maud fitz John (e1236-1301) [S756] [S925]
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Attributes
ClaimDetailEvidence
GenderFemale
NameIsabel Bigod [S756]
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NameIsabel [S954]
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FatherHugh Bigod, 3rd Earl of Norfolk (e1178-1225) [S756] [S954]
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MotherMatilda Marshal (e1190-1248) [S756] [S954]
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Timeline
ClaimDateDetailAgeEvidence
Birthest 1213 (1208-1218)
 
Marriage 2ndaft Dec 25, 1230Sir John fitz Geoffrey, Lord of Hallamshire (e1207-1258) [S954]
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Marriage 2ndaft 1230Sir John fitz Geoffrey, Lord of Hallamshire (e1207-1258) [S756]
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Sources
IndexTitle
[S756] Weis, Frederick Lewis, "Ancestral Roots of Sixty Colonists Who Came To New England before 1700, 7th Ed." (Genealogical Publishing Co., Inc., Baltimore, 1999).
[S954] Cawley, Charles, "Foundation of Medieval Genealogy (Medieval Lands - England Earls 1067-1122)" (2006-7 (v1.1 Updated 23 April 2007)).
Kinship Lines for Isabel Bigod
Spouse/PartnerDegreeRelationshipMRCA
Sir John fitz Geoffrey, Lord of Hallamshire (e1207-1258)93rd Cousin 1x removedGilbert fitz Richard I, Lord of Cardigan (e1060-~1117)
Sir John fitz Geoffrey, Lord of Hallamshire (e1207-1258)93rd Cousin 1x removedAdelisa de Clermont (e1061-)
Sir John fitz Geoffrey, Lord of Hallamshire (e1207-1258)219th Cousin 1x removedFulk II, Count of Anjou (e912-958)
Sir John fitz Geoffrey, Lord of Hallamshire (e1207-1258)219th Cousin 1x removedGerberge (e913-<952)
Sir John fitz Geoffrey, Lord of Hallamshire (e1207-1258)2310th Cousin 1x removedHerbert de Vermandois II, Count of Vermandois and Troyes (~880-943)
Sir John fitz Geoffrey, Lord of Hallamshire (e1207-1258)2310th Cousin 1x removedLiegarde of France (e887-)