Top 2 pair but raised on river

[JDErickson]

MP3 16/0/.25

Party Poker 3/6 Hold'em (6 max, 9 handed) converter

Preflop: Hero is BB with A[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/club.gif[/img].
UTG calls, <font color="#666666">3 folds</font>, MP3 calls, CO calls, <font color="#666666">2 folds</font>, <font color="#CC3333">Hero raises</font>, UTG calls, MP3 calls, CO calls.

Flop: (8.33 SB) 2[img]/images/graemlins/diamond.gif[/img], K[img]/images/graemlins/heart.gif[/img], J[img]/images/graemlins/club.gif[/img] (4 players)
Hero bets, UTG calls, MP3 calls, CO calls.

Turn: (6.16 BB) A[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">Hero bets</font>, UTG folds, MP3 calls, CO folds.

River: (8.16 BB) 7[img]/images/graemlins/spade.gif[/img] (2 players)
Hero bets, MP3 raises, Hero ???

Of course Hero will call, but who raises here?