 However, on 11 December 722 Fergal and numerous nobles of the Uí Néill were slain at the disastrous Battle of Allen (modern County Kildare) by the Leinstermen.The battle was preserved in the 10th century saga "Cath Almaine".According to the saga "Fáistine Fergaile meic Máele Dúin" ("Fergal mac Máele Dúin's Prophecy") his son Áed Allán was born by a daughter of the high king Congal Cendmagair in an illicit union while the mother of his son Niall Frossach was of the Ciannachta.