Much to the relief of the Plantagenets, the following year, de Lacy himself was assassinated at Durrow by an Irishman, Giolla Gan Mathiar Ó Maidhaigh.

Gerald of Wales said that the Irish then complained to their overlords — men such as Domhnall Mór Ó Briain — of how John was "an ill-mannered child… from whom no good could be hoped".

John alienated many of the island's resident elites (Irish and English), lost most of his army in battle or through desertion, and returned to England less than a year after arriving.

Upon his departure, his father Henry granted the office of justiciar to the Baron John de Courcy, who had massive influence in Ulster.

However, the death of his brother, Geoffrey II, Duke of Brittany, in France cancelled these plans and John did not return to Ireland until his second expedition in 1210.

The expedition has attracted much historical debate due to the lack of government records available and the subsequent reliance on sources such as the Irish Annals and the writings of Gerald.