Brad Paisley surprised Carrie Underwood and thousands of her fans by singing "Remind Me" with her at Nashville's Bridgestone Arena on Sunday night (Sept. 23). Underwood was just one verse into the song when Paisley's vocal came over the sound system, causing Underwood to stop mid-song and quickly look behind her. She burst into tears when she saw Paisley walking toward her and knocked off his white cowboy hat when she hugged him. Although Paisley's appearance obviously caught her off guard, she only missed a few lines of the song before regaining her composure and finishing their duet. Paisley flew back to Nashville following his set at the iHeartRadio music festival in Las Vegas earlier that day.