The 45-year-old Little Britain comedian made a dig at the 46-year-old judge’s risque outfit, which featured both a navel-grazing neckline as well as being backless.
Following a performance by Welsh schoolgirl choir Angelicus Celtis, who he praised for a stirring rendition of Jerusalem, he made the jibe.
He told them: “I think you’re really connecting with people because of your incredible talent.
“We talk all the time about looking for an act for the Royal Variety Show – well, the royals would absolutely love this!
“I really like the way you perform and you’re so very classy. None of you are wearing a really inappropriate, low-cut top.”
His words led Amanda to burst out laughing as she saw the huge irony in his words.
David’s remarks come in contrast to that of head judge Simon Cowell, who told the choir they were “too serious” and wanted to see the young girls act their age and be more "fun".
David Walliams took a swipe at Amanda Holden's outfit on Britain's Got Talent
Amanda Holden wears a stunning outfit for Britain's Got Talent
I really like the way you perform and you’re so very classy. None of you are wearing a really inappropriate, low-cut top
Amanda’s daring ensemble certainly got viewers talking this evening as many raised an eyebrow at the amount of flesh on display on the family-orientated show.
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Many took to social media to discuss the outfit as one person tweeted: “For a family friendly show think it's outrageous what Amanda Holden is wearing. So not appropriate. BGT sort it out #BGT #shocking.”(sic)
Two other users continued: “What an inappropriate dress @AmandaHolden #BGT #familyshow,” and: “Great boobs @AmandaHolden but please put them away for a family show #AmandaHolden #BGT #bgt2017.”
Amanda Holden flashed the flesh on Britain's Got Talent Amanda Holden in pictures Fri, June 2, 2017
Amanda Holden and some of the best and sexiest pictures of the famous British presenter and BGT judge.
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Amanda Holden wowed in a seriously sexy dress at the BGT finals
Tonight saw another group of acts take to the stage for the fourth and penultimate live semi-final show of Britain’s Got Talent.
There were performances from teen singing sensation Reuben Gray, John Parnell, Paws with soul, Jonny Awsum, Merseygirls, The Pensionalitiesm Ryan Tracey as well as the choir.
In the end, Alesha Dixon’s Golden Buzzer act the Merseygirls and The Pensionalities were sent through and will be joining finalists Kyle Tomlinson, mind reading act DNA, magician Matt Edwards, Issy Simpson, Tokio Myers and comedian Ned Woodman.
Britain’s Got Talent continues on ITV tomorrow at 7.30pm.