Surprise!!! 3-bet on river

[LukeSLTS]

Turning Stone 15/30, usual semi-tight/passive game.
Villain 1: He is one of the looser players at the table but passive.
Villain 2: He is a supertight rock. The only hands he raises preflop are AA and KK, with the occassional QQ to mix it up.
I have a TAG image, but today I have had better cards so I have been raising a lot more and have taken down the blinds about five times in the last 1.5 hours.

I get A [img]/images/graemlins/diamond.gif[/img]K [img]/images/graemlins/diamond.gif[/img] UTG and raise villain 1 calls in MP and villain 2 calls on the button. Villain 1 can have any pair or any two cards ten or higher. Villain 2 has TT+, AJ+, and possibly KQ. The SB folds and BB calls.

The flop is A [img]/images/graemlins/heart.gif[/img]9 [img]/images/graemlins/diamond.gif[/img]6 [img]/images/graemlins/diamond.gif[/img]

I bet MP raises (he would do this with an ace or better but never as a semibluff), and button 3-bets (minimum holding is AQ), BB folds, and I cap.

Turn is K [img]/images/graemlins/club.gif[/img] and I bet, both villains call.

River is a 4 [img]/images/graemlins/club.gif[/img] and I bet, MP raises and button 3-bets. What the hell just happened? If there had been more action on the turn I would lay this down right away but this river has me baffled.