• Married:
• Died: After 1126

  Research Notes:

Robert of Torigny names "unum filium Guillermum et tres filias" as the children of "Robertus comes Moritonii uterinus frater Willermi regis", specifying that one unnamed daughter (mentioned first) married "Andreas de Vitreio". A charter dated to [1110] records that "Andreas dominus Vitriaci castri et frater eius Philippus et uxor ipsius Andreæ…Agnes, cum filiis suis Roberto, Gervasio et Elia" confirmed the foundation of Sainte-Croix de Vitré. It is possible that Agnes de Mortain was “Agnete amita mea” in the following charter: “Willelmus...dux Aquitanorum” donated “ecclesiam S. Juliani de Stapio...ecclesiam S. Mariæ de Clida” to Notre-Dame de Saintes “et abbatissæ Sibillæ amitæ meæ” by charter dated “XII Kal Sep”, signed by “eadem abbatissa Sibillla, et comitissa Tholosæ avia mea, et Agnete amita mea, et Arembergi de Volvent monacha...Petro episcopo...”. The charter does not specify the year but can be dated to [1126/27], given that Duke Guillaume X succeeded his father in 1126 and that the successor of Pierre Bishop of Saintes (assuming that he can be identified as the subscriber “Petro episcopo”) is named in a document dated 1127. The donor in the document is identified as Guillaume X Duke of Aquitaine.... [There] are good arguments for identifying “abbatissæ Sibillæ amitæ meæ” as his great-aunt, sister of his grandmother Emma de Mortain. The key to identifying the subscribers to the document appears to be the presence of the donor’s maternal grandmother who would, it seems, not normally be involved in a donation by the duke of Aquitaine unless she had some interest in the property donated. If that is correct, “Agnete amita mea” would, logically, have subscribed only if she also had an interest in the same property. The best explanation is that the three subscribers were sisters who were the only surviving representatives of the Mortain family and joint holders of an interest in the properties donated. The main difficulty with this hypothesis is that Agnes’s husband was still alive at the time: it is therefore unclear why he would not have subscribed the document in place of his wife. The churches in question have not been identified. It should be pointed out that it is not obvious how the Mortain or Montgommery families, based in Normandy, would have held interests in churches which were presumably located in the Saintonge area of the duchy of Aquitaine. Another possibility is that the subscriber of the [1126/27] charter was Agnes, [probably illegitimate] daughter of Guillaume VIII Duke of Aquitaine, who succeeded Sibylle as abbess of Notre-Dame de Saintes in [1134/37]. However, in that case the potential common interest in the donated properties would not apply and it is then difficult to understand the reason for Agnes subscribing the document. ¹