After the death of his wife, Gormlaith, a devestated Toirreldcah O'Brien had shut himself inside his private rooms, refusing all visitors save his son, Tadg O'Brien, who found himself compelled to administer his father's domains. By the beginning of the year 1081, with Toirreldach's self-imposed exile still under way, rumors began to fly around the court that the seventy-one year old ruler was in fact now gravely ill and nearing death. These rumors would later be confirmed by Tadg, who sent messengers to deliver the somber news to his brothers.
Now that Toirreldach's illness was common knowledge at court, all began to wonder who would succeed the great man. Muirdertach was still the official heir, but Toirreldach's preference for his brother Donnchad was well known and he could name a new successor at any time. This was feared to be a likely occurrence by Muirdertach and his supporters given Donnchad's exemplary performance leading Munster's armies in Wales. Before long, Munster's court was divided between the two factions and each were looking to Tadg to tip the scales, it being widely believed that a word from Toirreldach's middle son would carry great weight with the old man.
This opinion was very accurate. Muirdertach was the eldest and had always been given what was his due as such. Donnchad, the youngest, had been given all of his parent's attention and love. Tadg, caught between the two, had been given something else that was,in many ways, just as important: his father's trust and respect. He alone of Toirreldach's sons had sat upon the inner council, and it was well known that no major decision was ever made by Toirreldach without his first having consulted his middle son. This fact had caused a small group to initially form around Tadg and press for him to stake his own claim to rule. Tadg had, however, quickly put an end to this. He knew that ruling Munster was not in his destiny. He could clearly see that the people supported his brothers, not him. The question was, which brother should he support?
As summer passed to fall, Toirreldach developed pneumonia, and his doctors informed the three brothers that the end was drawing near. That night, Tadg was visited by each of his brothers. As one would expect, they wished to discuss the succession. Muirdertach pointed out to him that he was eldest and Munster was his birthright. He wanted Tadg only to press their father to give him what was his. Donnchad pointed out that he was the champion of the people and that his military prowess would be desperately needed if Munster was to bring all of Ireland under it's control. Both of them, naturally, promised that Tadg would be well rewarded for his assistance. What neither of them understood, however, was that Tadg cared little for their promise of reward. He had long ago resigned himself to his small role in the world, and had dedicated himself first to Munster, and then to his father's vision of a unified Ireland. His decision would be based solely on what was best for Ireland, not on which brother offered the biggest reward. If anything, his brothers' power plays only left him feeling disgusted. They obviously cared only for themselves, and had little regard for the fact that their father was on his deathbed.
In December of 1081, Toirreldach called Tadg to attend him. The old man had surprised everyone by having hung on this long, but he knew that his end was near. He was prepared to name a formal successor and wanted to ask Tadg's opinion, as everyone knew he would. After a brief discussion of the merits of each brother, Tadg pointed out that Donnchad's wife was past birthing age and had given him no sons. Muirdertach, on the other hand, already had a son and heir. In the interest of long term stability, the two men decided that Muirdertach was the best choice. In the last proclamation of his long rule, Toirreldach confirmed his eldest son as the heir to all of his holdings. Five days later, on December 23 1081, Toirreldach O'Brien passed away. After a somber funeral, his body was laid to rest beside that of his wife, Gormlaith, in a small church that he had founded in his youth.
On New Years Day 1082, Muirdertach O'Brien assumed the throne of Munster. Though the majority of Munster's people and court felt that Toirreldach had made the wrong choice, Muirdertach would quickly prove them wrong. Under his rule, Munster would reach new heights.