William de Braose, Lord of Abergavenny (ca. 1197 - May 2, 1230) was the son of Reginald de Braose. He succeeded his father in his various lordships in 1227, including Abergavenny and Builth.
He was captured and imprisoned (as an act of retaliation) by Llywelyn the Great, ruler of most of Wales, in 1229, but was given relative freedom because he was related to the prince by marriage in several ways - his daughter, Isabella, was married to Llywelyn's only legitimate son. However, in the following year, Llywelyn is said to have discovered that his wife, Joan, had committed adultery with William, and had William hanged on May 2, 1230. Joan herself was later pardoned.
Sources:
1. Abbrev: Griffith J.E. Pedigrees of Anglesey and Caernarvon Title: Griffith J.E. Pedigrees of Anglesey and Caernarvonshire families Note: Call number: Page: 301
Lord Brecknock, Abergavenny William de Braose 
