A little math help?

[nik]

Playing in a tourney a few weeks ago. Got dealt AA, make the standard raise, and get put all in my the chip leader. He turns over KK. Flop comes down A, 7, 9 rainbow. I'm feeling very good at this point. No flush possibilities. The turn comes K. The River comes K. I'm having nightmare's about this. [img]/images/graemlins/smile.gif[/img]

What are the odds of him catching running kings?