In 1587 Dónal, now twenty-six years old, decided to claim leadership of the clan. He petitioned the authorities in Dublin, using primogeniture as the basis for his claim, whereby the oldest son should inherit his father's title regardless of his age at the time of his father's death. The English Commission in Dublin was receptive to his argument since they preferred to have the English procedure followed throughout Ireland. In addition Sir Owen had lost influence in Dublin due to implication in the Desmond Rebellion. The Commission found in favor of Dónal, who was now The O'Sullivan Beare. Sir Owen had to be content with Whiddy island and part of Bantry. He died the following year and was succeeded by his son, another Sir Owen.