It's no secret that Carrie Underwood is a diehard Blockhead, so when New Kids on the Block brought their Total Package Tour to Nashville's Bridgestone Arena on May 17, she was most certainly there. She even graced the stage for a very special "Happy Birthday" dedication to Jordan Knight!

"We decided to bring Carrie Underwood out to sing Happy Birthday to Jordan," Donnie Wahlberg tells the crowd in the above video, capture by a fan.

Before Underwood kicked off the song, she urged those in attendance to sing along with her, "like you mean it." While balloons were shown on the screen behind her, the entire arena erupted in a singalong of "Happy Birthday" to Jordan. That wasn't all the band had up their sleeves, though.

"Since Carrie's one of our biggest fans for her entire lifetime and drives around the country to see us, which we still can't believe happened, now we're going to let Jon sing 'Happy Birthday' to you even though it's not your birthday," Wahlberg added.

NKOTB shared a photo with their special guest on Instagram, telling Underwood, "Always great to see you."

Underwood, meanwhile, also spent some time chatting with opener Paula Abdul and posed for a quick photo opportunity. "Well, look who I ran into backstage at #TheTotalPackage Tour! So cool to watch her do her thing!" she writes. She also shared videos from the concert, taken from seats high above the crowd.

The country singer has been seen NKOTB on the road when she can, and in 2015 gushed about the guys and thanked them for playing her favorite song live in concert after they called her out and dedicated “Single,” a duet with Ne-Yo from their 2008 album, The Block, to her.

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