Who was the last king to set foot on US soil?

It obviously wasn't George III, he was too fat to waddle over there in those pre-revolution days. Indeed, it might never have actually happened. And this is specifically a question about kings, so female monarch's won't suit my purpose. Anyone who can give me a good answer will probably deserve a good 50 points, as it's a toughie. One last point. I'm talking about an official visit, as king, so Edward, of Mrs Simpson fame doesn't count.