General Notes

William de Briouze, son and heir by 1st wife.  He m. Eve, daughter an in her issue coheir of William (Marshal), Earl of Strigul and Pembroke.  He d. 2 May 1230, being hanged by Llewelyn [ap Iorwerth, his step-mother's father] abovenamed.  His widow d. bef. 1246.  [Complete Peerage I:22]

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William de Braose fell victim to the jealousy of Llewellyn, Prince of Wales, who suspecting an intimacy between him and the princess, his wife, King Henry's sister, invited him to an Easter feast, and treacherously cast him in prison at the conclusion of the banquet. He was soon afterwards put to death with the unfortunate princess.  [I believe Joan Plantagenet died 6 or 7 years later.]

From The Genealogist article by Wm. Addams Reitwiesner

He was discovered in Joan's chambers, accused of being her lover, and promptly and publicly hanged. While the story that William and Joan were lovers has been generally accepted, the Annals of Margam (in T. Gale, ed , Historiae Britannicae et Anglicanae Scriptores XX (Oxford, 1687), 2-18, [anno] MCCXXX) implies that the "intimacy" was devised by Llywelyn to avenge himself on William for political injuries inflicted not only by William but by the entire Braose family; the execution was hailed by the Welsh as a vindication of a blood-feud against the Braoses dating from at least 1176. Indeed, shortly after the execution Llywelyn wrote to William's widow Eva and to William Marshal, Earl of Pembroke, Eva's brother, stating, in effect, that so far as he was concerned, the intended marriage between Llywelyn's son Dafydd and Eva's daughter Isabella could go forward as planned, and that he could not have prevented the Welsh magnates from taking their vengeance. See J. Goronwy Edwards, Calendar of Ancient Correspondence concerning Wales (Board of Celtic Studies of the University of Wales, History and Law Series, 2)(Cardiff, 1935), pp 51-52, nos. XI.56a, 56b. The marriage in fact took place three months later.