Dafydd ap Llywelyn (c.1208–46), prince of Gwynedd (1240–6). The only son of Llywelyn ab Iorwerth, prince of Gwynedd, and Joan, daughter of King John, he was declared heir to his father's principality. This was recognized by Henry III (1220) and the pope (1222), and Welsh nobles swore fealty to him (1226, 1238); he did homage to Henry III (1229). Dafydd's marriage to Isabella, daughter of William de Braose, incorporated Builth into Llywelyn's domain. Dafydd's elevation alienated his illegitimate elder brother Gruffydd, and tension grew as their father aged; in 1239 Dafydd deprived Gruffydd of some lands and imprisoned him. When Llywelyn died (1240), Henry III determined to curb Dafydd's ambitions. At Gloucester (15 May) he was knighted by the king, who received his homage; but Llywelyn's acquisitions outside Gwynedd were withheld and the homage of other Welsh nobles was reserved to the king. These humiliating terms were imposed on Dafydd in agreements at Gwerneigron and London (29 August and 24 October 1241), whilst Gruffydd was handed over to Henry III, who exploited him against Dafydd. After Gruffydd died (1 March 1244) while trying to escape from the Tower of London, Dafydd resolved to resist the king: he gained support from Welsh nobles, sought endorsement from the pope, wrote to the king of France, styled himself prince of Wales, and resumed his father's policy of creating a modern, feudal principality. Henry III launched an expedition against him (1245), but it was Dafydd's sudden death at Aber (25 February 1246) that halted his ambitions. He was buried in Aberconwy abbey. He had no heir and Gruffydd's sons claimed Gwynedd; for the moment, however, the crown's triumph was complete, as the treaty of Woodstock (30 April 1247) illustrated.

Ralph Alan Griffiths