Dafydd ap Llewelyn
Llewelyn ap Iorwerth's son and heir took the throne of his father's kingdom without apparent trouble. Henry II affirmed Daydd's right to rule, but he insisted that the rulers of other Welsh kingdoms were his own vassals, not Dafydd's.
This gave men like Grufudd ap Gwenwynwyn freedom to regain lands they had ceded to Dafydd's father Llewelyn. Henry was concerned that Dafydd's elder brother Grufudd could be a focus for discontent in Gwynedd, so he forced the new king to hand Grufudd over.
The elder ap Llewelyn was imprisoned in the Tower of London. On St. David's Day, 1244 he attempted to escape by climbing down a rope of sheets knotted together. The sheets broke, and Grufudd plunged to his death.
Dafydd struck up an alliance with nobles in Deheubarth, and Henry retaliated by invading Gwynedd. Dafydd appealed to the pope, but Innocent IV valued his income from England more than he wanted Wales, and refused to accept Dafydd as his vassal.
Dafydd promptly died, providing Henry with the right to claim Gwynedd, but it was by no means certain that the English king had the strength to enforce his claim.