Fitz

This is seen, for example, with Otuer fitz Count, illegitimate son of Hugh d'Avranches, Earl of Chester (the continental title count being the equivalent of the English earl), while several illegitimate children of the Norman and early Angevin kings were called fitz Roy, which means "son of the king" in Anglo-Norman French.

The Irish surname FitzGerald, for example, is thought to derive from Gerald de Windsor, a Cambro-Norman nobleman whose son and grandson were involved in the Norman invasion of Ireland.

From the Stuart era (1603–1714) and later, there was a revival of the adoption of fitz surname forms, particularly for illegitimate children of kings, princes, or high nobility, for example Fitzroy for the children of Charles II and one of his mistresses, the Duchess of Cleveland; FitzJames, for the illegitimate children of king James II (1685–1688) and Arabella Churchill; FitzClarence for those of Duke of Clarence, later King William IV (1830–1837) by Mrs. Jordan; and FitzGeorge, for the sons born to the legally prohibited marriage of Prince George, Duke of Cambridge (1819–1904) with Sarah Fairbrother, who would refer to herself as Mrs. FitzGeorge.

This practice by the late royalty gave rise to the erroneous belief that historical instances of Fitz surnames also denoted illegitimacy, which was not the case.

Ben Jonson's play The Devil Is an Ass includes the eccentric and foolish Norfolk squire named Fabian Fitzdottrell, a name evoking the dotterel, viewed by Jacobeans as a foolish bird, while Anthony Trollope's 1862 novel Orley Farm features the fictional rakishly aristocratic figure Lord John Fitzjoly.

More recently, Robin Hobb has written a series of fictional fantasy novels featuring a royal bastard, the assassin FitzChivalry 'Fitz' Farseer.

(Names are variously spelled with or without a space and capital letter after "Fitz-") Fitz is also a stand-alone German surname originating in the Palatinate region of Germany.