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 was named "protector and defender of the realm" while King Henry VI was suffering from mental illness and remained in the position until 9 February 1455. During the subsequent Wars of the Roses between the houses of York and Lancaster the Duke of York was killed at the Battle of Wakefield in 1460. Fotheringhay Castle remained a favoured residence of the family after Richard's death: Cecily often entertained guests there and in 1469 Elizabeth Woodville, Edward IV's queen, resided at the castle. On 11 June 1482, the Scottish prince, Alexander Stewart, Duke of Albany made a treaty at the castle