Guy and Constance had two daughters, Alix of Thouars and Katherine, Dame of Vitre, in 1201. Constance died in childbirth.
Between 1198 and the time of her death delivering twin daughters, Constance acted as regent for her young son Arthur I, Duke of Brittany. Constance had abdicated her ducal throne in Arthur's favour in 1194. Once Duke Arthur I died in 1203, he was succeeded by his infant maternal sister, Alix of Thouars. Guy served as Regent of Brittany for his infant daughter Alix, Duchess of Brittany from 1203 to 1206.
In 1206 Philip II took the regency of Brittany himself, much to the consternation of the Breton nobles. [b]
^In 1196 Constance had been imprisoned by her second husband Ranulph de Blondeville, 4th Earl of Chester. However, the Bretons rose in revolt to protest her imprisonment and Ranulph was forced to release her. Ranulph and Constance divorced in 1199. Once home in Brittany, Constance married Guy.
^The young Arthur had already sworn fealty to Philip as king in 1199; Philip now chose this opportunity to exert direct influence in Brittany. In 1213 Philip II of France arranged for Alix of Thouars to marry Peter of Dreux.