PokerStars No-Limit Hold'em, $0.50 BB (7 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

MP1 ($21.20)
MP2 ($39.25)
CO ($51.60)
Button ($50)
SB ($36.60)
Hero ($54.30)
UTG ($54.60)

Preflop: Hero is BB with K, A.
UTG raises to $1, 5 folds, Hero raises to $3, UTG raises to $5, Hero calls $2.

Flop: ($10.25) J, 6, 3 (2 players)
Hero checks, UTG checks.

Turn: ($10.25) 2 (2 players)
Hero checks, UTG checks.

River: ($10.25) K (2 players)
Hero ???

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Opponent is a 70/25 over 20 hands, I've never seen him re-raise before. Earlier I played a unraised pot with him where he checked behind on the river with two pair.

What's your river move?