The King of Connacht, Cathal Crobhdearg Ua Conchobair (O'Connor), fought a successful counter-attack against Anglo-Norman castles in Munster (including de Burgh's castle of Castleconnell). Further fighting led to the loss of three castles and property, all of which was eventually retrieved (with the exception of much of Connacht). Connacht In 1200, "Cathal Crobhdearg Ua Conchobair went into Munster, to the son of Mac Carthy and William de Burgh to solicit their aid." This marked the start of William de Burgh's interest in the province. Cathal Crobhdearg Ua Conchobair (King of Connacht, 1190–1224) faced much opposition (mainly from within his own family) and wished to engage de Burgh's aid to further secure his position. In 1201, William and Ua Conchobair led an army from Limerick to Tuam and finally to Boyle. Ua Conchobair's rival, Cathal Carragh Ua Conchobair, marched at the head of his army but was killed in a de Burgh/Ua Conchobair onslaught after a week of skirmishing between the two sides. William and Ua Conchobair then travelled to Iar Connacht and stayed at Cong for Easter. Here, William de Burgh (and the sons of Rory O'Flaherty) conspired to kill Ua Conchobair but the plot was foiled (apparently by holy oaths they were made to swear by the local Coarb family). However, when de Burgh demanded payment for himself and his retinue, a battle broke out with over seven hundred of de Burgh's followers said to have been killed. William, however, managed to return to Limerick. In the following year, 1202, William returned and took revenge for the destruction of his army a year earlier. He took the title "Lord of Connacht" in 1203. Death He died during the Winter of 1205/06 and was interred at the Augustinian Priory of Athassel in Golden which he had founded c.1200. The Annals of the Four Masters recorded his passing thus: "William Burke plundered Connacht, as well churches as territories; but God and the saints took vengeance on him for that; for he died of a singular disease, too shameful to be described." Family William de Burgh's wife was the daughter of Domnall Mór Ó Briain, King of Thomond, whom he married in around 1193. A late medieval genealogy found in the Book of Lecan (dated c.1397-1418) records his marriage to an unnamed daughter of Donmal Mor mac Turlough O'Brien, and the descent of the Earls of Ulster and Clanricarde from their son