At a recent stop on Kelsea Ballerini's tour with the Jonas Brothers, Ballerini was joined by a surprise guest: Thomas Rhett.

At the Hollywood Casino Amphitheatre in Chicago on Sunday (Sept. 12) — which was also Ballerini's 28th birthday — Rhett shocked the audience, showing up to join the "I Hate Love Songs" singer for her hit song "Half of My Hometown."

Get our free mobile app

The original song features Kenny Chesney, but Rhett filled his shoes nicely for the live performance.

Ballerini later commemorated the pop-up duet on Instagram, which prompted a fan to comment: "Omg when I saw u guys perform I almost died it was so good."

"Half of my hometown, but always on the hometeam. Thanks for singing with me tonight TR," Ballerini writes to caption the image.

While it was a surprise to the audience that Rhett would make a guest appearance, it isn't surprising that he would do so for Ballerini, who is his good friend.

"We've toured together, written together, been insecure and celebrated together, had double dates, and have just become like brother and sister," she told People in 2019.

Ballerini will be performing dates on the Jonas Brothers' Remember This Tour through the end of October in a trek that takes her all across the United States. Shortly after wrapping up the tour, Ballerini will make her debut as an author with the release of Feel Your Way Through: A Book of Poetry on Nov. 16.

Rhett is mid-tour himself, with dates stretching into early October, ending with an Oct. 9 show in Raleigh, N.C.

See the Top 50 Country Duets of All Time!