routed them. Niall Culanach, now king of Inishowen (a sub-kingdom within Tyrone) saw an opportunity following this and offered his assistance to King Edward I to destroy O'Neill and alleged that he had some protection from the authorities in Dublin. O'Neill however later that year received a lenient pardon for his part in the feud, even though it would drag on until 1276 when the de Mandeville's were defeated. At the battle of Desertcreat in 1281, the forces of O'Neill along with those of the new seneschal of Ulster, Thomas de Mandeville, decisively defeated and killed Donnell Óg O'Donnell and many of his sub-chiefs greatly curbing the power of his Cenél Conaill rivals. Death and succession O'Neill reigned until his death in 1283 when he killed by Brian McMahon of Airgíalla and Gilla Ísa O'Reilly. O'Neill was succeeded by Donnell O'Neill, son of Brian O'Neill of the battle of Down. His son Brian with the backing of Richard Óg de Burgh, 2nd Earl of Ulster, would replace Donnell as king of Tyrone in 1291. References Clandeboye 13th-century Irish monarchs O'Neill dynasty 1283 deaths Assassinations in Ireland