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 rebelled against Henry III late in 1220, and in January the following year captured Fotheringhay Castle, installing his own garrison. He attacked several other castles the same month, but the capture of Fotheringhay was Forz's only success. According to a royal letter he "furtively and seditiously seized the castle of Fotheringhay ... devastating and plundering our land and violently disturbing and infringing our peace and that of our kingdom". Faced with a massing royal army, Forz fled north and Henry III took Fotheringhay and Castle Bytham. Henry III retained control of the castle, and it remained in royal possession until