of Brycheiniog, was hanged by the lord Llywelyn in Gwynedd, after he had been caught in Llywelyn's chamber with the king of England's daughter, Llywelyn's wife." A letter from Llywelyn to William's wife, Eva de Braose, written shortly after the execution enquires whether she still wishes the marriage between Dafydd and Isabella to take place. The marriage did go ahead, and the following year Joan was forgiven and restored to her position as princess. Until 1230, Llywelyn had used the title princeps Norwalliæ 'Prince of North Wales', but from that year he changed his title to 'Prince of North Wales and Lord of Snowdonia', possibly to underline his supremacy over the other Welsh princes. He did not formally style himself 'Prince of Wales' although as J. E. Lloyd comments "he had much of the power which such a title might imply." Final campaigns and the Peace of Middle 1231–1240 In 1231, there was further fighting. Llywelyn was becoming concerned about the growing power of Hubert de Burgh. Some of his men had been taken prisoner by the garrison of Montgomery and beheaded, and Llywelyn responded by burning Montgomery, Powys, New Radnor, Hay, and Brecon before turning west to capture the castles of Neath and Kidwelly. He completed the campaign by recapturing Cardigan castle. King Henry retaliated by launching an invasion and built a new castle at Painscastle, but was unable to penetrate far into Wales. Negotiations continued into 1232, when Hubert was removed from office and later imprisoned. Much of his power passed to Peter de Rivaux, including control of several castles in south Wales. William Marshal had died in 1231, and his brother Richard had succeeded him as Earl of Pembroke. In 1233, hostilities broke out between Richard Marshal and Peter de Rivaux, who was supported by the king. Llywelyn made an alliance with Richard, and in January 1234 the earl and Llywelyn seized Shrewsbury. Richard was killed in Ireland in April, but the king agreed to make peace with the insurgents. The Peace of Middle, agreed on 21 June, established a truce of two years with Llywelyn, who was allowed to retain Cardigan and Builth. This truce was renewed year by year for the remainder of Llywelyn's reign. Death and aftermath Arrangements for the succession In his later years, Llywelyn devoted much effort to ensuring that his only legitimate son, Dafydd, would follow him as ruler of Gwynedd