The unlikely pop opera duo saw 16-year-old pop starlet Charlotte perform with Opera tenor Jonathan after their music teacher thought they'd be a good pairing.
"She thought it would be good to try us out together and we both sounded quite good when we sang what we did," Charlotte explained to the judges.
But their audition got off to a poor start, with Simon remarking as they walked out: "Just when you thought it couldn't get any worse."
Jonathan went on to reveal battles with weight and bullying, after being noticeably quiet in his chat with the judges.
He confessed: "I’ve always had a problem with my size since I can remember and when I was in primary school it was back then really that I had the mick taken out of me and it kind of damaged my confidence quite a bit. When people would say something to me, it would just take a little piece out of me in a sense.
"Charlotte’s been a really big help for me, in terms of confidence and making me a better performer and I really don’t think I would be going up on stage today if I didn’t have Charlotte by my side."
Pal Charlotte added: "I’m quite protective of Jonathan if I was there and someone stood there and said something to him, I couldn’t sit there with my mouth shut. Before you make a judgement on someone I think you really need to know them, it’s cliché, it’s not judging a book by its cover, you’ve got to read what’s inside.
After the performance, a clearly impressed Simon was left almost speechless.
He reacted: "Wow, wow, wow. Oh my god. Erm, Alesha?"
Alesha commented: "It’s not very often that that happens, that you can move an audience like that - You sing beautifully together. It was world class."
David added: "A pop voice and an opera voice together, it was incredible."
But Simon then dropped a bombshell for the pair.
He told them: "Ok this is what I think, Charlotte I think you’re good but Jonathan you are unbelievable. I mean seriously you have an outstandingly good voice.
"I like the fact that this works as a duo but I worry Charlotte whether you’re gonna hold him back."
After a tense pause, Jonathan declared: "Well we’ve come on here as a duo and we’re gonna stay here as a duo."
It was four yeses from the panel, and a place at next month's callbacks for the pair.
Watch [tag]Jonathan Antoine[/tag] & Charlotte Jaconelli's audition on Britain's Got Talent below...