Guillaume was the son of Guillaume II de Derval and Anne de Rostrenen. The date and place of his birth have not been found.
His wife was Aliénor de Châteaubriant. They were married, but the date and place have not been found. Their only known child was Bonabes II (?-?).
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Anne de Rostrenen |
Riwallon II de Rostrenen |
Pierre I de Rostrenen |
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Theophanie de Lanvaux |
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| Attribute | Date | Description | Details | Source | Multimedia | Notes |
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| Nobility Title | seigneur de Derval |