William de Braose, Lord of Abergavenny (c. 1197 to 1204 – 2 May 1230) was the son of Reginald de Braose by his first wife, Grecia de Briwere (born 1186) from Stoke in Devon. He was the tenth Baron Abergavenny and an ill-fated member of a powerful and long lived dynasty of Marcher Lords. William de Braose was born in Brecon. The Welsh, who detested him and his family name, called him Gwilym Ddu, Black William. He succeeded his father in his various lordships in 1227, including Abergavenny and Builth.

William married Lady Eva Marshal, daughter of William Marshal, 1st Earl of Pembroke. They had four daughters:

  1. Isabella de Braose (born c. 1222), wife of Prince Dafydd ap Llywelyn
  2. Maud de Braose (born c. 1224 - 1301), wife of Roger Mortimer, 1st Baron Wigmore another very powerful Marcher dynasty.
  3. Eleanor de Braose (c. 1226 - 1251), wife of Humphrey de Bohun and mother of Humphrey de Bohun, 3rd Earl of Hereford.
  4. Eve de Braose (c. 1227- July 1255), wife of William de Cantelou.

He was captured by the Welsh forces of Llywelyn the Great, leader (Welsh, "Tywysog") of most of Wales, in fighting in the commote of Ceri near Montgomery, in 1228. William was ransomed for the sum of £2,000 and then furthermore made an alliance with Llywelyn, arranging to marry his daughter Isabella de Braose to Llywelyn's only legitimate son Dafydd ap Llywelyn.

However on a later visit to Llywelyn during Easter 1230 William de Braose was found in Llywelyn's private bedchamber with Llywelyn's wife, Joan, Lady of Wales.

The Chronicle of Ystrad Fflur's entry for 1230 reads:

"In this year William de Breos the Younger, lord 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."

Llywelyn had William publicly hanged on 2 May 1230, probably at Crogen near Bala.

With William's death by hanging and his having four daughters, who divided the de Braose inheritance between them and no male heir, the titles now passed to the junior branch of the de Braose dynasty, the only male heir was now John de Braose who had already inherited the titles of Gower and Bramber from his far-sighted uncle Reginald de Braose.

William's wife Eva continued to hold de Braose lands and castles in her own right, after the death of her husband. She was listed as the holder of Totnes in 1230, and was granted 12 marks to strengthen Hay Castle by King Henry III on the Close Rolls (1234-1237).

Source: http://en.wikipedia.org/wiki/William_de_Braose,_10th_Baron_Abergavenny