Anybody speak Latin?

Okay, I am finally ready to commission the sign that will be planted in stucco above The Secret Lair's door.

Problem is, I'm not certain of exactly what it should say. The closest I've been able to come, and this comes from a forum discussion about two years ago, is "Ultimum Responsum Regibus."

Sounds about right to me, but I am not entitled to an opinion since I slept through my single semester of high school Latin and that was in the 'sixties.

So - can any of you educated types tell me? What is the proper latin translation of "Ultimate Answer to Kings?"

(BTW, the sign will be quite cool. Engraved sandstone, and cheap!)