[Shandrax]

I assume that he called on 4th street with (maybe too) many hands, yes. On the river it is not that easy to call it "just a bluff" since any overcard to a jack can technically win the pot.

All our hero needs to do to break even is to beat 43 more or less legitimate combinations. A-K, A-Q and K-Q make up for 48 combinations.

The question is, would your opponent bet such hands on the river? With ace high, maybe he can make a small pair like 7-7 fold. Don't forget that he could have had 6-6 also. That's another 12 combinations and a very legitimate hand.