The America's Got Talent season 12 finale was chock full of celebrity cameos, but none were quite as unexpected as Derek Hough's surprise appearance.
On Wednesday's star-studded finals results show, each of the 10 acts that competed in Tuesday's finals took the stage yet again for an encore performance before the winner was announced -- including the wildly inventive Ukrainian dance crew, Light Balance.
Performing a shorter version of the routine that earned them the coveted Golden Buzzer from host Tyra Banks during the audition rounds at the start of this season, Light Balance pulled out all the stops to show why they are one of the most impressive LED dance groups ever.
And when the lights came up, it was revealed that they got a little help from a special guest.
WATCH: 'America's Got Talent': Amazing Ukrainian Dance Crew Gets the Golden Buzzer From Host Tyra Banks!
While Light Balance basked in the glory of their epic performance, Hough surprised the crowd as he pulled off his LED-lined headgear and smiled for the audience. Even the judges looked stunned.
"This is crazy! Have you been here the entire season?" Banks asked, laughing.
"The whole season!" Hough joked as he struggled to catch his breath. "It's very hot in [these clothes], so hats off to these guys. It's amazing."
WATCH: 7 Mind-Blowing Performances From 'America's Got Talent' Season 12 Premiere
Hough was just one of a number of guest stars on Wednesday's finale, which also included live performances from Kelly Clarkson and Shania Twain.
For more on Light Balance's Golden Buzzer-worthy performance early this season, check out the video below.