Ailill Flann Bec, son of Fiachu Muillethan

Fiachu Muillethan

Fiachu Muillethan or Fiachu Fer Da Liach , son of Éogan Mór, was a legendary king belonging to the Deirgtine, the proto-historical ancestors of the Eóganachta dynasties of Munster...

, was an Irish

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

 dynast belonging to the Deirgtine

Deirgtine

The Deirgtine or Clanna Dergthened were the proto-historical ancestors of the historical Eóganachta dynasties of Munster. Their origins are unclear but they may have been of fairly recent Gaulish derivation...

, the proto-historical ancestors of the historical Eóganachta

Eóganachta

The Eóganachta or Eoghanachta were an Irish dynasty centred around Cashel which dominated southern Ireland from the 6/7th to the 10th centuries, and following that, in a restricted form, the Kingdom of Desmond, and its offshoot Carbery, well into the 16th century...

 dynasties of Munster

Munster

Munster is one of the Provinces of Ireland situated in the south of Ireland. In Ancient Ireland, it was one of the fifths ruled by a "king of over-kings" . Following the Norman invasion of Ireland, the ancient kingdoms were shired into a number of counties for administrative and judicial purposes...

. He was the father of Luigthech, also known as Lugaid

Lugaid

Lugaid is a popular medieval Irish name, thought to be derived from the god Lug. It is borne by a number of figures from Irish history and mythology, including:High Kings of Ireland...

, and thus the grandfather of Conall Corc

Conall Corc

Corc mac Luigthig, also called Conall Corc, Corc of Cashel, and Corc mac Láire, is the hero of Irish language tales which form part of the origin legend of the Eóganachta, a group of kindreds which traced their descent from Conall Corc and took their name from his ancestor Éogan Mór. The early...

. Another son of Ailill Flann Bec may have been Dáire Cerbba

Dáire Cerbba

Dáire Cerbba was an Irish dynast of uncertain origins, named in many early and late sources as the grandfather of the semi-mythological Mongfind and Crimthann mac Fidaig, and the most frequently named early ancestor of the historical Uí Liatháin and Uí Fidgenti...

, but there is evidence against this.

He was adopted by and succeeded his elder brother Ailill Flann Mór, who left no issue.