Also, a tip to save you agony on the next boss, dude.
When the boss charges some spell and goes into a stance for about half a minute, just attack him, and keep attacking him. Unfortunately, one would think that doing such a stance would mean to go into defensive mode, but this game is stupid so it's the opposite - attack him and his attacks power lessens.
This will save you a lot of time attempting time and time again (it's a long fight, it took me 16 minutes to kill him) only to end up in failure. It's not even a hard fight, just a long and dumb one.