Folded AA on river on paired flop

[jkiddy07]

Full Tilt No-Limit Hold'em, $0.30 BB (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

CO ($59.45)
Button ($52.40)
SB ($10.75)
BB ($57.15)
UTG ($102.05)
Hero ($60)

Preflop: Hero is MP with A, A.
[color=#CC3333]UTG raises to $0.6</font>, [color=#CC3333]Hero raises to $2.4</font>, [color=#666666]1 fold</font>, Button calls $2.40, [color=#666666]2 folds</font>, UTG calls $1.80.

Flop: ($7.65) 6, K, K [color=#0000FF](3 players)</font>
UTG checks, [color=#CC3333]Hero bets $4.75</font>, [color=#CC3333]Button raises to $9.5</font>, UTG folds, Hero calls $4.75.

Turn: ($26.65) 9 [color=#0000FF](2 players)</font>
Hero checks, [color=#CC3333]Button bets $8.4</font>, Hero calls $8.40.

River: ($43.45) T [color=#0000FF](2 players)</font>
Hero checks, [color=#CC3333]Button bets $19.2</font>, Hero folds.

Final Pot: $43.45