First off I must agree with Gergery, you never should've played the hand. Nevertheless, once you get called on the turn, your opponent reasonably has only 1 of 3 hands: set, two pair, flush draw (or combo of any 2). Once the river hits and he raises full pot, not calling, he can really only have one hand, Broadway. Your same king high straight might make a move to take it down, but usually not knowing you can come back over the top. It's a very tough laydown, but without any info on your opponent I believe it must be made.