WASHINGTON — If you thought “SNL 40” was wild, the after-party was nuts.

Jimmy Fallon spoke with “did that just happen” awe as he recounted the star-studded affair Tuesday night on “The Tonight Show.”

The venue had a stage set up filled with instruments in case any of the artists wanted to perform.

What followed was an impromptu celebrity concert.

Paul McCartney jammed with Taylor Swift on “Shake it Off” and “I Saw Her Standing There.”

Then came performances by The B-52’s, Elvis Costello and Debbie Harry from Blondie.

Finally, at the urging of Dave Chappelle, Fallon dared Prince to come up on stage.

The crowd parted like the Red Sea and Prince “floated to the stage,” according to Fallon, to perform “Let’s Go Crazy,” paraphrasing his opening lyric with the line: “Dearly inebriated.”

Watch the insane behind-the-scenes video below: