Carrie Underwood had a big surprise in store for fans during her Nissan Stadium set at CMA Fest 2019 on Friday (June 7): The singer called rock icon Joan Jett to the stage for a hard-charging medley of Jett's greatest hits.

Together, Underwood and Jett performed "I Hate Myself for Loving You," "Bad Reputation," "I Love Rock 'n' Roll" and more. The first of those three songs, Underwood is especially familiar with: "I Hate Myself for Loving You" was re-worked into "Waiting All Day for Sunday Night," NBC's Sunday Night Football theme song from 2006 through 2016. Underwood was that song's official singer from 2013 on, preceded by Faith Hill (2007-2012) and Pink (2006).

Backstage, Underwood shared her excitement about the collaboration with The Boot and other outlets. "I get to sing with Joan Jett, guys!" she gushed. "I'm super excited ...

"The stars just aligned. It was like, 'What if Joan Jett came to CMA Fest? Let's ask her!'" Underwood explained of how the pairing came to be. "So she's here. The coolness has arrived, and I'm hoping some of it rubs off on me."

Underwood admits she's a huge fan of Jett's on many levels, "the music, first and foremost." But as she learned more about the iconic performer, her admiration only grew.

"The more I got to know her and see just how much of a trailblazer she was, for not just women in her genre of music, but of women in music in general. I mean, I'm a fan on every level: personally, professionally, musically," Underwood says. "I'm honored she's heard my name before, and that she agreed to come sing with me."

Despite her iconic status, Underwood relates, Jett was focused on making sure her performance would be at its best during the days leading up to CMA Fest. "It's not nervousness -- it's just wanting to do well," the country star clarifies. "She's like, 'I know this isn't my world. I hope they know the songs,' and I'm like, 'Are you kidding me?! Of course they know the songs.'

"I know it's not [her] audience, but it is, you know? Because they're like me, and they've heard the songs. They're gonna know every word to every song," Underwood goes on to say. "So it's gonna be so much fun for me to get to show off our people to her, and show off our crowd and how amazing they're gonna be to her."

CMA Fest 2019 runs through Sunday (June 9). A TV special featuring performances from the event will air in early August.

CMA Fest Day 2: See More From Carrie Underwood + Joan Jett

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