Carrie Underwood Geeks Out Over Singing Happy Birthday to NKOTB's Danny Wood and Jordan Knight

Carrie Underwood is geeking out over the New Kids on the Block!

The country star had a total fangirl moment after singing “Happy Birthday” to NKOTB members Jordan Knight and Danny Wood during the group’s Total Package Tour stop in Nashville, Tennessee, on Wednesday.

RELATED: Carrie Underwood Surprises Nashville Predators Fans With National Anthem Performance

The clearly surreal stage experience left Underwood in shock.

“Um…did I just sing happy birthday to @dannywood and @jordanknight on stage with the NEW KIDS ON THE BLOCK?!?! Yup!” she excitedly tweeted.