The castle was seized in 1264 without fighting by Simon de Montfort during the civil conflicts in the reign of Henry III, and was seized back in turn by the former High Sheriff of Cornwall, Sir Ralph Arundell, in 1265. After some persuasion, Isolda de Cardinham granted the castle to Henry III's brother, Richard of Cornwall in 1270. Richard died in 1271, and his son Edmund took over Restormel as his main administrative base, building the inner chambers to the castle during his residence there and titling it his "duchy palace". The castle in this period resembled a "miniature palace", with luxurious quarters and piped water. It was home to stannary administration and oversaw the local, profitable tin-mines in the village.