The singer/songwriter surprised the crowd by joining Luke during his Thursday, July 31 performance at the festival in Chicago's Grant Park, teaming up to do the song that's spent nine weeks atop the Billboard Hot 100.
"Ordinary" is also the top-selling track in the U.S. this year. Already one of the "most talked about moments of the entire festival," the Lollapalooza version's been viewed more than 85 million times across social media platforms. You can check it out now on YouTube.
This isn't Alex's only foray into the country world. Jelly Roll appears on the track "Bloodline" on his You'll Be Alright, Kid album.