The Third Prince did not die easily. The struggle that resulted as he fought for his life was not pretty or noble, it was not a glorified thing when dealing with death, and when you added Rowan's bitterness against the Third Prince and his wish to end the great weight hanging over his neck since the time of his birth, it did not create a bearable sight for the weak of mind.
Rowan did not find back, millennia of anger and suffering were returned, all of which was channeled under a cold rage that meant every single move he made was perfect.
Reduced to a mortal by the bridge, and overwhelmed by Rowan's power and weapons, the Third Prince was slowly worn down. With a single arm and lying flat on his back, he fought with a skill that defied meaning, his arsenal of weapons was seemingly endless, but Rowan at this moment had gone insane.