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 as well as other properties in Huntingdonshire. Possession of the castle descended through the Scottish princes until the 13th century. Shortly after King John was excommunicated, he demanded his barons send him hostages to ensure their loyalty. In 1212, he used this as leverage against David, Earl of Huntingdon and Prince of Scotland, to acquire Fotheringhay Castle. He wrote to the earl, saying "You have given us your son as a hostage, therefore we require you to yield to us your castle at Fotheringhay". This is the first documented reference to the castle. The period 1208 to 1214 saw John