Before I looked down, I was going to say it smells like KQ, and if one was a diamond, you're not getting him to fold. If both were diamonds (couldn't be), he's not going anywhere.
Look at the hand from his perspective. He open raises with KQ. You 3-bet him, so he has to call. You go to the flop heads-up.
Flop is
![The Six of Diamonds [6d]](https://pofex.com/images/smilies/6d.gif)
.
I'll assume he actually had
![The Queen of Hearts [Qh]](https://pofex.com/images/smilies/Qh.gif)
, for argument's sake. You could be 3-betting with anything, but since you bet the flop, it damn sure ain't JJ, since he's probably sure you wouldn't bet flopped quads. You could be on AA (Yahtzee), AK, AQ, KK, QQ (the last two he's not putting you on because he'd be in trouble. He sees overcards and a backdoor flush draw. The BDFD is worth about 1.5 outs in reality, plus his two live cards (which only work if he doesn't put you on KK or QQ, AK, or AQ) gives him 7.5 outs. He's getting 8.5-to-1 odds on his call on the flop when he believes he has 5.26-to-1 odds of hitting a hand. To him, his call is correct.
The turn brings
![The Ten of Diamonds [Td]](https://pofex.com/images/smilies/Td.gif)
. He now has a flush draw (assuming you don't have the
![The Ace of Diamonds [Ad]](https://pofex.com/images/smilies/Ad.gif)
), and an open-ended straight draw, plus his overcards. He has 9 outs for the flush, though the
![The Ace of Diamonds [Ad]](https://pofex.com/images/smilies/Ad.gif)
in your hand would counterfeit them. Cut those in half. So, 4.5 outs for the flush, 3 other 9's and 3 other A's for the straight, and he could also have 3 Q's and 3 K's for an overpair if you're playing with a pair under JJ. He has an conservatively estimated 15 outs here, so he's got odds all day to call your turn bet. He then hits on the river and takes the pot.
If he doesn't read you on AA, KK, QQ, JJ, AK, or AQ, he has outs a plenty in his mind.
It really sucks to have AA cracked like that, but in limit it's so hard to limit a player's ability to call on a draw...
With that board, I flat call the river and save a BB.