The rest of the earl's life was mainly occupied by endeavours to maintain his influence, and by an undying feud with his son Shane (John), arising out of his transaction with Henry VIII.
Shane O'Neill (C. 1530-1567) was a chieftain whose support was worth gaining by the English even during his father's lifetime; but rejecting overtures from the earl of Sussex, the lord deputy, Shane refused to help the English against the Scottish settlers on the coast of Antrim, allying himself instead with the MacDonnells, the most powerful of these immigrants.
In his private character Shane O'Neill was a brutal, uneducated savage.
Hugh then appealed to Shane O'Neill, who invaded Tyrconnel at the head of a large army in 1557, desiring to make himself supreme throughout Ulster, and encamped on the shore of Lough Swilly.
Calvagh was then recognized by the English government as lord of Tyrconnel; but in 1561 he and his wife were captured by Shane O'Neill in the monastery of Kildonnell.