50NL AK hits top pair - funky reraise from villain on river

[dlorc]

saw flop|<font color="#C00000">saw showdown</font>

<font color="#C00000">Hero ($53.11)</font>
BB ($28.55)
UTG ($23.92)
MP ($16.80)
<font color="#C00000">CO ($47.40)</font>
Button ($11.44)

Preflop: Hero is SB with A[img]/images/graemlins/club.gif[/img], K[img]/images/graemlins/diamond.gif[/img].
<font color="#666666">2 folds</font>, <font color="#CC3333">CO raises to $0.75</font>, <font color="#666666">1 fold</font>, <font color="#CC3333">Hero raises to $2</font>, <font color="#666666">1 fold</font>, CO calls $1.25.

Flop: ($4.25) 2[img]/images/graemlins/diamond.gif[/img], K[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $2.5</font>, CO calls $2.50.

Turn: ($9.25) T[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $4.5</font>, CO calls $4.50.

River: ($18.25) J[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $10</font>, <font color="#CC3333">CO raises to $20</font> Hero ???

The pot is now $48.25 so we are getting 4.825-1 to call here.

Villain is 31.5/4.35/0.41, his AF is a little misleading because his river AF is 6 but his aggression on all other streets is very low. He has 22% WTSD and I have ~100 hands on him so its not like river aggression isnt abnormal from him.

What range do we assign him on the river, and given the pot size do we call, reraise or fold on the river?

I think this is a genuinely tough spot in a session I recorded earlier, I believed he was on a weaker king on the flop/turn so I was giving him KJ, K9,K8. - QQ is just about possible also and perhaps AQ..

In hindsight after writing this I feel I have the correct answer but I think the discussion might be interesting anyway.