New Kids on the Block really did deliver the "total package" during their Total Package Tour stop in Nashville on Wednesday night (May 17). Surprise guest Carrie Underwood threw down a "Happy Birthday" sing-a-long for NKOTB members Jordan Knight and Danny Wood, who celebrated their birthdays on Wednesday and Sunday (May 14), respectively.

Readers can press play above to watch Underwood's surprise performance. The NKOTB guys reciprocated with a birthday tune for Underwood ... even though her birthday is in March.

Underwood outed herself as a "Blockhead" in 2016, when NKOTB serenaded her with a song at another of their live shows.

Underwood had quite the busy night at Wednesday night's show: In addition to feeling as though she was back in middle school, the country superstar also reunited with former American Idol judge, Paula Abdul backstage at the show. Underwood and Abdul first met when the would-be Idol winner auditioned for the show in 2005.

But Underwood wasn't the only country act to take in NKOTB's Music City show: Big & Rich also hung out backstage and took the stage with the boy band to sing their own hit "Save a Horse, Ride a Cowboy.".

NKOTB are joined by Abdul and Boyz II Men on their current Total Package Tour. The trek us a followup of sorts to their 2013 Package Tour.

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