Despite his immortality he was to end up dying. Hercules stopped to vist Pholus. Hercules was thirsty and persuaded Pholus to open a jar of wine that was the common property of the centaurs. The other centaurs smelled the wine and came running. A fight broke out between Hercules and the centaurs. Chiron took no part in the fight but, was accedentally wounded by Hercules. As an immortal Chiron could not die but, lived in terrible pain.
Chiron then chose to trade his life for the release of Prometheus.