[Mathieu]

Sometimes when a PFR checks it means he has flop a monster, but here KK is too unlikely. He could have QQ or JJ and be trying to get too showdown for cheap. Maybe he want's to avoid going broke in this hand.

For some reason, AK or AA just doesn't feel right with that flop check.

I think I bet and call down if raised. It's too risky to fold TPGK on this board vs someone who could be steaming or at least is playing somewhat desperately. You only need to be good about 20% by the river to justify a call down.

I am not sure if it is correct to worry about him checking behind and wanting to get to showdown cheaply. I got the impression that he would want to check behind with weaker pairs, but call down if we bet.