Jennifer Lawrence, Amy Schumer dance atop Joel's piano

Actresses Jennifer Lawrence and Amy Schumer made a surprise appearance at a Billy Joel concert Thursday night.

Witnesses immediately took to social media to report the unforeseen event; Schumer's colleagues -- including her sister Kim Caramele -- also posted videos on Instagram.

Joel's "Uptown Girl" was a prominent tune in Schumer's screenwriting debut, Trainwreck.

According to reports, the stars and their crews rehearsed all day to get their silly cameos just right.

BFFs Jennifer Lawrence and Amy Schumer just took their friendship to the next level: piano-dancing buddies!

The comedian, 34, and Hunger Games actress, 25, joined Billy Joel onstage during his Chicago concert on Thursday – and in true Lawrence-Schumer form, the ladies made it quite a show to remember.

They climbed on top of Joel's piano and danced to his hit song "Uptown Girl" – a tune that was prominently featured in Schumer's comedy hit Trainwreck.

"Billy came out for his encore and started singing 'Uptown Girl,' " a concertgoer told PEOPLE. "And then Amy and [Jennifer] came out with some others for the song! Eventually Amy and [Jennifer] were dancing on Billy's piano. Absolutely loved it."

Naturally, the crowd went wild as soon as the two stars hit the stage.

"So I was just at the billy Joel concert and in the middle of a song JENNIFER LAWRENCE AND AMY SCHUMER RANDOMLY WALKED ONSTAGE omg asdfghjkl," Tweeted another fan from the crowd.

    So I was just at the billy Joel concert and in the middle of a song JENNIFER LAWRENCE AND AMY SCHUMER RANDOMLY WALKED ONSTAGE omg asdfghjkl