 Edmund, the Earl of Lancaster, gained possession of the castle in 1267, and it remained in the hands of the earldom and later duchy of Lancaster until 1825.Edward I's conquest of Wales in 1282 removed much of Grosmont Castle's military utility, although it was besieged in 1405 during the Glyndŵr Rising.By the 16th century it had fallen into disuse and ruin.