Constance was the daughter of Bertha, daughter of Conan III, Duke of Brittany and Matilda FitzRoy, and of Alan the Black, Earl of Richmond, younger son of Stephen of Penthièvre and Havoise of Guingamp.
[1] She was the sister of Duke Conan IV of Brittany and Enoguen, Abbess of Saint-Sulpice.
[1] On 15 September 1146, her father died and two years later her mother married Odo II, Viscount of Porhoët, who became regent of Brittany during Conan IV's minority.
Constance married secondly Alan III, Viscount of Rohan,[4] and founded the Abbaye Notre-Dame de Bon-Repos with him on 23 June 1184.
If Constance did marry William of Tournemine, she was the mother of: With Alan III, Viscount of Rohan, she had: