The troupe gave an energetic performance but it was there exit from the stage that left the Geordie dup scratching their heads.
As the group, who were dressed as harlequins, headed backstage the soundtrack to Ghostbusters could be heard playing in the background.
When the camera cut to Dec, he could be seen laughing as he looked to his co-host and questioning: "Ghostbusters?"
He shot a puzzled look at the judges and off stage before shaking his head in confusion.
Britain's Got Talent: TNG Characters left the presenters baffled by their exit music
Britain's Got Talent: Dec could be seen looking confused by the Ghostbusters music
Ant also questioned the music blunder as he noted the strange song choice: "Ghostbusters? What?!"
The ITV talent show then cut to a short break as the pair giggled about the soundtrack for TNG Characters exit from the stage.
Later in the evening, the presenters were left far from impressed when judge David Walliams took a rude swipe at them.
While commenting on singer Jamie Lee Harrison's performance, the 45-year-old joked: "It just shows there is talent that can come out of Newcastle," before shooting a mischievous look at Ant and Dec.
Britain's Got Talent: The pair could be seen shaking their heads in disbelief Britain's Got Talent: Most memorable moments Mon, May 1, 2017
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Dance act Just Us get the golden buzzer
Britain's Got Talent: Ant and Dec were shocked when David took a swipe at them
The duo could be seen shaking their head in disapproval as the rest of the judging panel laughed at David's remark.
Tonight's semi-final saw the Missing People Choir and Daliso Chaponda sail through to the final with Jamie just missing out in third place.
Britain's Got Talent final airs Saturday on ITV at 7.30pm.