from Military History magazine:
Irish Triumph at Yellow Ford
"Russell was only too glad when the Irish agreed to a truce in southeast Ulster, which lasted until the summer of 1597. During that time, however, the English were alarmed to learn that a priest named Piers O'Cullen of Clogher had sailed to Spain, bearing a letter dated September 19 and signed by O'Neill and O'Donnell. The letter beseeched the Spanish king to send 2,000 to 3,000 men, along with arms and money, to Ireland "to restore the faith of the [Catholic] Church and so secure you a kingdom." By seeking aid from England's principal rival, the Irish coalition was raising the stakes of the war"
Was O'Cullen from Clogher, or just priest there? Was he related to Bishop Cullen?