From A Concise History of Ireland by Maire and Conor Cruise O'Brien, p 47:
The Hiberno-Norman lords, by contrast, throve. [in the 1300's] The Irish resurgence had made them indispensable to the Crown and the creation of the three great earldoms, Desmond (Fitzgerald), Ormond (Butler), and Kildare (Fitzgerald), towards the middle of the century sealed the King's admission of this fact, but the forfeiture and outlawry only very shortly afterwards of the first Earl of Desmond demonstrates how dubious their surety could be. Indeed, the King's subjects in the colony complained only less of the exactions of the great earls than of the depredations of their Irish counterparts. . . . From the very outset the Norman knights had intermarried with the Irish and were quick to grasp the political usefulness of a custom such as fosterage, under which the children of noble houses were brought up from infancy in other noble families with whom it was desirable to cement alliances.
The Hundred Years War and the Wars of the Roses in turn meant that no English king up to Henry VIII could give his individual attention to Ireland, much less finance a reconquest. the Yorkist cause was indebted to the Desmonds, who in 1462 had routed the Lancastrian forces led by their rivals of Ormond. It was the zenith of the Desmond power, but six years later too close an association with the native Irish brought the Earl to the scaffold, and the King was forced to fall back on the other branch of the Fitzgerald family, that of Kildare. The Great Earl of Kildare became for over thirty years the uncrowned King of Ireland, in spite of a brief interlude at the Lancastrian restoration when Sir Edward Poynings (1495) effectively subordinated the business of the Irish parliament to the English Crown. The Great Earl was succeeded in his functions by his son Garrett Og (the younger) who in time came to fall foul of Henry VIII.

Killed in the same battle as his father.