William FitzWilliam (Lord Deputy) William FitzWilliam (Lord Deputy) Sir William FitzWilliam (1526–1599) was an English Lord Justice of Ireland and afterwards Lord Deputy of Ireland. In 1587, as Governor of Fotheringhay Castle, he supervised the execution of the death sentence on Mary, Queen of Scots. He was the Member of Parliament for Peterborough and represented County Carlow in the Irish House of Commons. He lived at Gainspark, Essex, and Milton Hall. FitzWilliam was born at Milton Hall, Northamptonshire, the eldest son of Sir William (d. 1576) and grandson of William Fitzwilliam, Sheriff of London, who had been treasurer and chamberlain to Cardinal Wolsey and
Fotheringhay Castle the reign of Edward II. During the Second Barons' War, Fotheringhay and Chester Castle were taken by Robert de Ferrers, 6th Earl of Derby. He held them from 1264 to 1265. Edward II granted Fotheringhay Castle to John of Brittany, Earl of Richmond. When John died in 1334, his granddaughter inherited Fotheringhay Castle, Mary de St Pol, the widowed countess of Pembroke. She died in 1377, and Edward III gave her property over to his son, Edmund Langley. In 1385, he was made Duke of York by the king and Fotheringhay Castle became his principal seat. According to John Leland