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Agnes FitzWilliam was born on an unknown date to William FitzNigel (-1134) and Agnes de Gant (-c1134) and died circa 1157 of unspecified causes. She married Eustace FitzJohn (-1157) .
Children
| Name | Birth | Death | Joined with |
| Richard FitzEustace (-1171) | 1171 England | Albreda de Lisours (-1193) | |
Siblings
| Name | Birth | Death | Joined with |
| Agnes FitzWilliam (-c1157) | 1157 | Eustace FitzJohn (-1157) | |
| Leuca FitzWilliam (-c1162) | 1130 England | 1162 England | Robert de Mohaut (-1162) |
| Matilda FitzWilliam | |||
| William FitzWilliam (-1149) | 1149 Normandy, France | ||