Óengus took the reigns of power to find the treasury of Brittany all but empty, while the penniless populace melted away against the plague. A fairly incompetent man, Óengus was at least a good fighter. His tall stature assured him dominance in single combat and was at first known as “the Tall.”
An ominous portent of the years to come, the Duke was excommunicated barely 3 years into his reign, in December of 1342. The reasons were purely political – the Duchy of Champagne and the de Vergy Dynasty that ruled it held tremendous sway over the Pope. In their attempt to seize Brittany and other Duchies, they were more than able to dole out spiritual punishments. Óengus was struck deeply by the blight, feeling that the once sacred Papacy had become corrupted and secular. Such ideas would eventually materialize into a new Christian denomination, but that will come soon.
In retaliation against the Duke Charles, Óengus ordered three assassination attempts on him – all failed. The attacks would prove needless in the end, as the Duke soon died of age on May 20, 1343. Charles’ heirs, fearing more intrigue, had the Pope offer a revocation of the excommunication – in exchange for a large indulgence, of course. To be blackmailed was the final straw for Óengus and on August 27, 1343, having formally rejected the Pope’s offer – he founded the Church of Brittany. Though quite indifferent from Catholicism, the Church of Brittany ignored the Pope, instead decentralizing the Church under the authority of several weaker Bishops – all answering to the Duke. In retaliation, the Pope declared Óengus not only excommunicated, but an apostate heretic as well.
Such religious turmoil shook the nobility of Brittany to the core. Many Counts desperately broke away, attempting to sever themselves from any association with the Duke. With an iron hand, Óengus crushed them all. By May of 1346, he had personal control over all of Brittany – having deposed all others of his dynasty. Afraid to relinquish his new power, Óengus dismissed the Feudal Contract, dismantled the powers of the nobility, and gave himself unprecedented control over both the Church and State. All of Brittany was now a personal fief of Óengus. Guy de Vergy, son of Charles, seeing Óengus was in a perfect position to be overthrown, mobilized his armies for a Crusade.
The war would go on for eight years and for the most part, Óengus proved a deadly opponent. Multiple times, armies from Champagne were completely obliterated. Guy de Vergy held firm, however, sure in the mass of manpower available in his holdings in Toulouse and elsewhere. His patience payed off and by March of 1352, he had his first victory in the sack of Saintonge. The Bretons, worn down by the war, were unable to stand up to the much large forces of Champagne. In October, Thouars fell, Nantes in January of 1353, and Rennes not long after.
Though Óengus tried desperately stave off the inevitable – which he did for another year, the last Breton stronghold in Penthievre fell on April 8, 1354. What happened to Óengus after this is unclear, but there is sparse evidence that he spent the rest of his days imprisoned in a French Bishopric. Brittany became yet another district of the large and powerful Archduchy of Champagne and Breton independence was now but a fantasy.
Dispersed or converted to Islam by the Berbers and without titles in Brittany, the Kernes disappeared into history.