However Flaithbertaigh Ua Néill, new king of the Northern Uí Néill and of the Cenél Eoghan, although having already submitted to Brian, seemed to have his own agenda. He was known for his continued aggression towards his neighbours despite having already submitted to Brian. In 1005, after Brian had departed, he attempted to exert his over lordship over the Ulaid, and seemingly wanted to punish them for submitting to Brian, to which the Northern Uí Néill were vehemently opposed. He attacked the kingdom, killing several kings and princes of the Ulaid. He also took several hostages.