William de Braose , 6th Lord de Braose, 10th Baron Abergavenny ^{1 2 3 4}

   Another name for William was William de Braiose.

  Research Notes:

Wikipedia (Humphrey de Bohun, 3rd Earl of Hereford)

Source: Ancestral Roots of Certain American Colonists Who Came to America before 1700 by Frederick Lewis Weis and Walter Lee Sheppard, Jr, ed. by William R. Beall & Kaleen E. Beall (Baltimore, 2008), line 177-8
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From http://www.castlewales.com/kington.html :
In 1201 King John "Softsword" (1199-1216) granted Kington Castle and Barony to his favourite Marcher Baron, William Braose of Radnor, Abergavenny and Brecon (d.1210) for the service of just ½ a knight! William in any case had been holding Kington Castle for many years in his capacity as Sheriff of Hereford. Early in 1208 King John demanded the castle back from William in a dispute over money and loyalty. The now aging Marcher baron complied, but soon afterwards with his 4 sons in attendance attacked the castle in a futile bid to retake it. With this action of defiance the Braose Clan were forced to flee to Ireland, and many met a terrible fate at the hands of King John.

In 1213 King John granted Kington Castle to his close supporter, Roger Clifford, and in May or June of 1215 the castle probably fell to the two remaining Braose brothers, sons of the great William Braose who had died in exile at Paris in 1210. In late July 1216 King John appeared at Hereford with an army and then marched on Hay on Wye. Here he called the last remaining Braose brother, Reginald, to him and offered him beneficial terms of peace. Reginald ignored the plea and John in vengeance burned the Braose town and castle of Hay on Wye. He then marched north through the Principality of Elfael to Kington and destroyed the castle and town on 4 August before continuing on his destructive path through the Braose Marcher territories. So ended the history of Kington Castle. The town eventually recovered on a new site down in the valley away from the castle and church, but no further fortifications were made at Kington. Instead, Reginald Braose, when he regained the favour of John's son, King Henry III (1216-72) in 1217 began a new fortress at Huntington to replace the now utterly destroyed Kington Castle.
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From Wikipedia - William de Braose, 10th Baron Abergavenny :

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 .

Dynastic history
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 .

Marriage and children
William married Lady Eva Marshal , daughter of William Marshal, 1st Earl of Pembroke . They had four daughters:
Isabella de Braose (born c. 1222), wife of Prince Dafydd ap Llywelyn
Maud de Braose (born c. 1224 - 1301), wife of Roger Mortimer, 1st Baron Wigmore another very powerful Marcher dynasty.
Eleanor de Braose (c. 1226 - 1251), wife of Humphrey de Bohun and mother of Humphrey de Bohun, 3rd Earl of Hereford .
Eve de Braose (c. 1227- July 1255), wife of William de Cantelou .

Career
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 .

Execution
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.

Legacy
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).

  Death Notes:

Hanged by orders of Llewelyn the Great , Prince of Wales for alleged adultery with the latter's wife, Joan, Lady of Wales . The hanging took place either at Crogen near Bala or near Llewelyn's castle at Abergwyngregyn.

William married Eve Marshal, daughter of Sir William Marshal 1st Earl of Pembroke and Isabel de Clare, on 2 May 1230 in Pembroke, Pembrokeshire, Wales. (Eve Marshal was born about 1194 in Pembroke Castle, Pembroke, Pembrokeshire, Wales, died before 1246 in England and was buried in Llanthony Priory, Monmouthshire, Wales.)