Who knew Jennifer Lawrence and Amy Schumer were such besties?

It was only the other day when we found out the two were costarring in and writing a movie together. Now they're executing choreographed flash mobs with Hall of Fame musicians.

Hollywood's new dynamic duo appeared on-stage with Billy Joel during his concert at Chicago's Wrigley Field on Thursday night. Schumer and Lawrence appeared with a group of folks, which included Schumer's sister, Kim Caramele, and "Inside Amy Schumer" writer Kyle Dunnigan, according to Entertainment Weekly.

Before we get into the actual performance, take a look at the rehearsal:

Joel gave a hint at the beginning of his hit song "Uptown Girl," when he asked, "Any of you guys seen the movie "Trainwreck"?

Here are a few shots of the duo climbing onto Joel's piano (Alert: In the first one, JLaw kissed Schumer's feet.)

Those kids. Watch the good times below (starting at about 2 minutes in):

SEE ALSO: Jennifer Lawrence and Amy Schumer co-writing screenplay to star as sisters

MORE: Amy Schumer explains why all her skirts in 'Trainwreck' were uncomfortably short

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