Mortimer was one of Llywelyn's rivals in the marches. When Humphrey de Bohun tried to take back Brycheiniog, which was granted to Llywelyn by the Treaty of Montgomery, Mortimer supported de Bohun. Llywelyn was also finding it difficult to raise the annual sums required under the terms of this treaty, and ceased making payments. In early 1274, there was a plot by Llywelyn's brother, Dafydd, and Gruffydd ap Gwenwynwyn of Powys Wenwynwyn and his son, Owain, to kill Llywelyn. Dafydd was with Llywelyn at the time, and it was arranged that Owain would come with armed men on 2 February to carry out the assassination; however, he was prevented by a snowstorm. Llywelyn did not discover the full details of the plot until Owain confessed to the Bishop of Bangor. He said that the intention had been to make Dafydd prince of Gwynedd, and that Dafydd would reward Gruffydd with lands. Dafydd and Gruffydd fled to England where they were maintained by the king and carried out raids on Llywelyn's lands, increasing Llywelyn's resentment. When Edward called Llywelyn to Chester in 1275 to pay homage, Llywelyn refused to attend. Llywelyn also made an enemy of King Edward by continuing to ally himself with the family of Simon de Montfort, even though their power was now greatly reduced. Llywelyn sought to marry Eleanor de Montfort, born in 1252, Simon de Montfort's daughter. They were married by proxy in 1275, but King Edward took exception to the marriage, in part because Eleanor was his first cousin: her mother was Eleanor of England, daughter of King John and princess of the House of Plantagenet. When Eleanor sailed from France to meet Llywelyn, Edward hired pirates to seize her ship and she was imprisoned at Windsor Castle until Llywelyn made certain concessions. In 1276, Edward declared Llywelyn a rebel and in 1277, gathered an enormous army to march against him. Edward's intention was to disinherit Llywelyn completely and take over Gwynedd Is Conwy himself. He was considering two options for Gwynedd Uwch Conwy: either to divide it between Llywelyn's brothers, Dafydd and Owain, or to annex Anglesey and divide only the mainland between the two brothers. Edward was supported by Dafydd ap Gruffydd and Gruffydd ap Gwenwynwyn. Many of the lesser Welsh princes who had supported Llywelyn now hastened to make peace with Edward. By the summer of 1277, Edward's forces had reached the