I think Aislephive is right - it's a weak king, and only a massive raise on the river is going to make him consider folding.

It *could* be 66-99 but I don't think so. I don't think it's a 5 as a 5 folds to the flop raise. I also don't think a missed flush bets like this at $25. K9-KJ is practically inevitable.