Fitzwilliam Castle was a castle in England, so named for its belonging to the family of Sir Ranulf Fitzwilliam. In 1215, it was the setting of a ruse orchestrated by the Tremas Master using Kamelion, whom he had impersonate John of England. (TV: The King's Demons)
The Fifth Doctor dines with the ostensible king of England at Fitzwilliam Castle. (TV: The King's Demons)