Jennifer Lawrence, Amy Schumer dance atop Billy Joel's piano

CHICAGO, Aug. 28 (UPI) -- Actresses Jennifer Lawrence and Amy Schumer made a surprise appearance at a Billy Joel concert Thursday night.

Lawrence, 25, and Schumer, 34 -- who wore casual clothes for their Chicago cameo -- walked on stage with several others during the singer's final song: "Uptown Girl." Eventually, the duo -- who recently announced they're working on a screenplay together -- climbed on top of Joel's piano barefoot and danced.

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.