Question: Who is Coirpre Mac Fogartaig's paternal grandfather?
Answer: Niall mac Cernaig Sotal

He belonged to the Uí Chernaig sept of the Síl nÁedo Sláine branch of the southern Uí Néill. He was King of Brega and was the son of Niall mac Cernaig Sotal (died 701) and great-grandson of the high king Diarmait mac Áedo Sláine (died 665). Coirpre mac Fogartaig (died 771) was a King of Brega of the Uí Chernaig sept of Lagore of the Síl nÁedo Sláine branch of the southern Ui Neill