Carrie Underwood is expecting her second child, but the superstar isn't letting it slow her down. The visibly pregnant star joined Keith Urban on stage at his concert in Nashville on Friday night (Aug. 24) to sing "The Fighter," and the hometown crowd loved every minute of it.

Underwood joined Urban mid-show for their duet, which originally appeared on his Ripcord album in 2016. She strode out from side stage to surprise the fans at the Bridgestone Arena as part of Urban's Graffiti U Tour stop, wearing a black shirt and blazer that did not hide her growing baby bump. At one point in the performance, she rubbed her bump as Urban sang the line, "You're beautiful, so beautiful."

The singer seemed to enjoy her guest spot as much as the audience, turning to social media afterward to write, "Will it ever suck getting to sing with @keithurban ??? No. The answer is no. Such an incredible and LOUD crowd at the @bridgestonearenaofficial tonight!!! I know you guys all had a blast! Thanks for having me up there with ya’ KU!"

Close up pictures from the concert show the singer might be further along in her pregnancy than fans knew.

Her appearance was just one of many tricks Urban had up his sleeve on Friday night. Early in the show, he brought his wife, Nicole Kidman, and her Big Little Lies co-star Reese Witherspoon to the stage, and his show was scattered throughout with appearances from Kassi Ashton, Kelsea Ballerini, a Belmont student named Ashley Sorensen, Larkin Poe and even the Tennessee State University marching band.

Underwood announced her second pregnancy on Aug. 8, the same day she revealed the cities and dates for her upcoming 2019 Cry Pretty Tour 360. She's set to release a new album, Cry Pretty, on Sept. 14.

What to Expect Now That Carrie Underwood Is Expecting

Relive Carrie Underwood's Best Baby Bump Pictures: