Credit: Larry Busacca/Getty Images For The Recording Academy Photo: Lady Gaga and Sir Paul McCartney at the 54th Annual GRAMMY Awards on February 12, 2012

Back in 2009, Alec Baldwin said Paul McCartney was his dream guest star on 30 Rock. Well, Alec got his wish — and a slap in the face. A collector's item!

Toward the start of 30 Rock's second live episode, which aired Thursday, April 26, Liz Lemon (Tina Fey) argued that TGS had to do a live show or they'd lose all the excitement and spontaneity. "I mean, that's the beauty of live TV," Liz said, "anything can happen."

Cue Kenneth (Jack McBrayer) opening the door to Jack Donaghy's (Alec Baldwin) office and saying, "There's a bathroom in here you could use, Sir Paul McCartney.” In entered the Beatles legend. The live audience cheered and Paul stopped to wave to them. He shook the stunned Jack's hand, slapped him in the face and just kept walking out another door in the office.

Sir Paul returned at the end of the live episode to say he slipped and hit his head in the bathroom and forgot who he was. "You're my boyfriend," Liz said. "We were just going to go call some people I went to high school with!"

Other NBC stars — including Community's Donald Glover, Parks and Recreation's Amy Poehler and Jimmy Fallon — also had cameos, and Mad Men’s Jon Hamm had two scenes, one as a hillbilly in a black-and-white clip of a past (fake) TV show and another as a newscaster alongside Alec Baldwin.

Speaking of Mad Men, Season 5 fans got "Zou Bisou Bisou" back in their heads, thanks to Paul (Will Forte) descending from the sky as an angel as he sang the French tune.

That song will never die!