Guillaume was the son of Joscelin de Beaumont-au-Maine and Constance FitzRoy. The date and place of his birth have not been found.
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Joscelin de Beaumont-au-Maine |
Raoul VII de Beaumont-au-Maine |
Hubert II de Beaumont-au-Maine |
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Ermengarde de Nevers |
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Henri I de Normandie |
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