Chronicle of the Princes of Wales is in Late Medieval Books.
Brut y Tywysogion aka Chronicle of the Princes of Wales. Edited by the Reverend John Williams ab Ithel, M.A. Rector of Llanymowddy, Merionethshire. 1860.
Immediately after that, Seisyll, son of Dyvnwal, was slain, through the treachery of the lord of Brecheiniog [William de Braose 4th Baron Bramber [aged 31]], in the castle of Abergavenny [Map] and with him Gruffudd his son, and many of the chieftains of Gwent. And then the French repaired to the court of Seisyll, son of Dyvnwal; and after seizing Gwladus his wife, they killed his son Cadwalader [aged 7]. And on that day there was the most miserable slaughter of the good people of Gwent. And after that most open and ílagitious treachery, none of the Welsh dared trust to the French
1230. One thousand two hundred and thirty was the year of Christ, when king Henry, having with him a vast armed host, sailed for France, with the intention of obtaining his right as to Normandy and Anjou and Poictou. And soon after that, on account of a storm and mortality, being disappointed of his purpose, he returned to England. That year, William Canton of Cemaes died. Then young Llywelyn, son of Maelgwn, died, on his estate in Gwynedd, and was honourably buried at Aberconway [Map].
1230. That year, William Bruse [aged 26] was hanged by Llywelyn [aged 58], son of Iorwerth "Drwyndwn aka Flat Nosed" Aberffraw, having been caught in the chamber of the prince, with the princess Jannet [aged 39], daughter of king John, and wife of the prince.