Count of Rennes

The Count of Rennes was originally the ruler of the Romano-Frankish civitas of Rennes. From the middle of the ninth century these counts were Bretons with close ties to the Duchy of Brittany, which they often vied to rule. From 990 the Counts of Rennes were usually Dukes of Brittany. In 1203 the county was integrated into the ducal demesne.

The County of Rennes was merged permanently into the Ducal crown of Brittany, and subsequently the crown of France, through Constance's descendants

...
Wikipedia