Kaley Cuoco sings 'Full House' theme, and John Stamos' reaction is priceless

Kaley Cuoco totally knows the "Full House" theme song, a show she never appeared in.

So how does "Full House" star John Stamos feel about Cuoco's show, "The Big Bang Theory," and its theme song?

Let's say he's a bit less of an expert.

"Here’s a little bit of sunshine that you didn’t know you needed — the adorable @kaleycuoco and I try to get through the Full House theme and so much more," Stamos captions a new video of himself (from W Magazine) and Cuoco on Instagram, and it's totally charming:

The duo has met up in what appears to be a black-walled room. She's carrying a hand-held fan and a sheaf of papers and trying not to fangirl too much.

"I'm living out all my dreams right now," Cuoco tells the camera. 'We're going to sing 'Full House' theme song with John Stamos."

"This is one of your dreams?" Stamos deadpans, and Cuoco tells him she knew he'd be there, so she came prepared. With lyrics.

And ... she's off! She's got more enthusiasm and hand gestures than anything else, and meanwhile, Stamos is left mugging for the camera, occasionally joining in for a line. At the end, he says, "That's terrible."

"That's perfect," she insists, and is next seen with a hand-held fan, trying to cool down. Apparently meeting Stamos is a sweaty business!

The video is called "Lyrical Improv," and was directed by journalist Lynn Hirschberg, who in 2008 was behind the camera for W's "Lynn Hirschberg's Screen Tests." This feels like a bit of a return to form.

Then he takes the reins and asks about her show's theme song! Which he hardly knows at all, except that it includes very large numbers. Fortunately, Cuoco also knows her own theme song. We then learn that the two of them live down the street from each other.

"We should work together," he says, and Cuoco says she's ready to go. "Not in show business," he continues. "A car wash or something."

Hey, we'd watch them together any time, anywhere!