Runner runner flush is the only way to bust my top set

So, with this guy pretty much just calling down the coming out of the woodwork on the river, I probably shouldn't have capped. Seemed like a real long-shot that I was behind to a flush, though =/

PokerStars 0.25/0.50 Hold'em (8 handed) Poker-Stars Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver Cards)

Preflop: Hero is Button with , . CO posts a blind of $0.25.
1 fold, UTG+1 calls, 1 fold, MP2 calls, CO (poster) checks, Hero raises, 2 folds, UTG+1 calls, MP2 calls, CO calls.

Flop: (9.40 SB) , , (4 players)
UTG+1 bets, MP2 calls, CO calls, Hero raises, UTG+1 calls, MP2 calls, CO folds.

Turn: (8.20 BB) (3 players)
UTG+1 checks, MP2 checks, Hero bets, UTG+1 calls, MP2 calls.

River: (11.20 BB) (3 players)
UTG+1 bets, MP2 folds, Hero raises, UTG+1 3-bets, Hero caps, UTG+1 calls.

Final Pot: 22.20 BB

Results in white below:
UTG+1 has Js Ks (flush, king high).
Hero has Kc Kh (three of a kind, kings).
Outcome: UTG+1 wins 22.20 BB.

NO CAPPING RIVER ALLOWED HERE!

yeah, the only time you're allowed to cap the river here is you can beat the flush or the straight. IE you need to have a Full house.

If it were the runner-runner flush and the 5 didn't also complete the Open Ended straight, I can imagine getting to 3 bets before the alarms are going off in my head, but comeon, the only BETTER card to come off on the river would be the 8s

I may cap the river, although it's probably close I probably call the river 3-bet and palmface

Yeah, the passive check-calling followed by a river donk when two draws complete. If you don't beat at least one of those draws you should make the crying call. If you have a read of him as anything at all tricky you might raise, but otherwise you are beaten here.

I raise-call the river. Most villains will check-raise that river if they hit their draw.