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
Mary, Queen of Scots of England, Elizabeth was recognised as her sister's heir, and Henry VIII's last will and testament had excluded the Stuarts from succeeding to the English throne. Yet, in the eyes of many Catholics, Elizabeth was illegitimate, and Mary Stuart, as the senior descendant of Henry VIII's elder sister, was the rightful queen of England. Henry II of France proclaimed his eldest son and daughter-in-law king and queen of England, and in France the royal arms of England were quartered with those of Francis and Mary. Mary's claim to the English throne was a perennial sticking point between her and Elizabeth