It has 4520 HP. Considering Scarmiglionë had 3523 HP in his second form, and you're fighting with just crappy Dark Knight Cecil, winning that fight with force is quite a feat.

It's funny, really, because the other fights in the game that you're not supposed to win are prettymuch fixed against you unless you're at Level 99 or thereabouts. When you fight Cain at Fabul, he has 65,000 HP, etc.