Later in 1162 Coilen, Ceallach and Conbrogha O'Dempsey were slain by Malachy O'Connor Faly in Killeigh. Dermot, Ceallach's nephew and son of Conboragha, became chief, slayed Malachy and became lord of Offaly. Few Leinster chiefs refused to attend Henry II's Dublin Assembly at Christmas 1171, but Dermot took part, and later defeated Strongbow after the invasion of Offaly. Monasterevan, formerly the Cistercian Abbey of Rosglas on the site of St Evin Abbey was founded by Dermot between 1170 and 1190, but died three years to later be succeeded by his son Hugh.