Britain’s Got Talent viewers were delighted as hosts Ant McPartlin and Declan Donnelly secretly auditioned for the show for the first time in 12 years.

As the auditions on the ITV competition series came to a close in Saturday’s programme, one more act appeared on the stage in a bid to win the judges’ approval.

An act called Disco Dogs, comprised of three people dressed as dogs, arrived on the stage in front of a large boombox, before starting a wild dance routine to songs including Who Let The Dogs Out, YMCA and Gangnam Style.

The audience and the judges were on their feet for the performance as others dressed as dogs appeared throughout the venue.

At the end of the audition, judge David Walliams told the three performers, who were still hidden within dog costumes, that it was “completely bonkers and completely Britain’s Got Talent”.

Simon Cowell said: “This is the sort of thing my son Eric would love. What a great end to the show this year, thank you.”

As the judges decided to send the act through, the three men took the heads of the costumes off to reveal themselves to be Ant and Dec and Britain’s Got More Talent host Stephen Mulhern.

Cowell, Walliams and their fellow judges Alesha Dixon and Amanda Holden were shocked at the prank from their co-stars.

Ant celebrated, saying: “We did it, we did it after all these years!”

Viewers were thrilled at the performance from Ant and Dec and Mulhern.

Taking to Twitter, one said that their surprising the judges “had made this year’s BGT”, while another said that it was “the funniest thing of the night”.

One fan tweeted: “Omggggg the dancing dogs were Ant n Dec and Stephen omg am cryingggg. I literally love #BGT so much.”

Another viewer said they were also fooled by the performance, writing: “I was more shocked at the fact that was Ant, Dec and Stephen than game of thrones plot twists #bgt #BritainsGotTalent.”

“That right there is the reason why the nation loves Ant & Dec – absolute geniuses #BGT #BritainsGotTalent,” another wrote.

The episode ended with the judges whittling down all of the successful act from this series down to a final 40.

Those who were chosen will take to the stage again in the live semi-finals next week, fighting for a place in the final.

Britain’s Got Talent continues on ITV at 7.30pm on Monday.