I would have liked to see you 3Bet him from the button there with that hand instead of just flatting as you're really not finding out much about his hand. He's playing 1/4 of his hands and has been raising every one of them, so you know that not every one has been strong. What was his CB%? I am guessing it was probably damn near 100% with the stats given, but once again, you should have raised him, as of course he's going to fire out a CB on that board. By the turn, I kind of think you've just let him get too many cards by letting him control the action, but you did pick up the flush draw. Although you're not getting the right odds
to call, even if you count the Kings as 3 extra possible outs(Against AQ maybe), then you are still only about 3.5:1 to hit. I say fold.
I'm guessing you either folded(right play) and didn't see what he had, or you called, then stacked off on the river and he showed AQ or A9