This chief of the O’Donoghues Mor suffered greatly for his bid at
independence from Mac Carthy Mor control. Even though he was the Mac Carthy
chief’s most honoured nobleman and leader of the forces of Desmond he
resented Mac Carthy hegemony and attempted to overthrow it.

He was unsuccessful in this and withstood a punishing raid;
‘Diarmait (Mac Carthy Mor) set his people to attack Seoan’s
stronghold…they carried off in equal numbers dogs and goats, hounds and
sheep, beeves and pigs, cauldrons and helmets, vessels of measure and
methers, ladles and breastplates, calves and kneading troughs, platters and
butter containers, swords and seives. Nevertheless, that is the most
foreign-like, the most disgusting, the most outlandish and most surprising,
the most wretched, the most monstrous and cruel, the most exotic and most
senseless thing that was done at that time or ever before in this Desmumu…
‘ AOI

Seoan was later taken from sanctuary and killed by Diarmait.