Watch Paul McCartney Serenade Jimmy Fallon with 'Birthday' During Barclays Center Show

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Paul McCartney performs on stage during his "One on One" tour at Madison Square Garden on Sept. 15, 2017 in New York City.  

You expect that Justin Timberlake will wish his old Camp Winnipesaukee pal Jimmy Fallon a happy birthday. But Paul McCartney? The former Beatle took some time out of his gig at Barclays Center on Tuesday night (Sept. 19) to call out Fallon and say happy birthday, and then, of course, sing "Birthday" to the 43-year-old Tonight Show host, who was in the audience losing his freakin' mind the whole time.

"Wait a minute, who's this guy?" McCartney says from the stage, looking out to spot Fallon in primo seats on the floor. "Hey, wait a minute, is that Jimmy, Jimmy Fallon?... Happy birthday Jim! Okay Jim, this is especially for you and the other people who who've got a birthday." Watch Fallon take selfies with wife Nancy Juvonen (and Saturday Night Live producer Lorne Michaels) sing along and lose his mind over the unexpected honor.

Watch the birthday boy fanboy below.