KSI leapt onto the judge’s table and slammed the golden buzzer after being impressed by Rafferty’s card trick which helped spell out the notes Don’t Stop Believin’ which he then played out in full on a piano.
Having secured the golden buzzer, Rafferty threw his hands in the air and thanked his family.
He told BBC Radio Solent: “I was not expecting it at all.
“We had to keep it secret for a while, with the golden buzzer.
“It’s not been an easy secret to keep from my friends but we managed to do it and managed to have a lovely watch party where everyone came. I couldn’t be happier with the result.”
The teenager said: “I’ve dreamt of being on this show for literally my whole life.
“Even standing on that stage was winning for me.
Rafferty has previously performed the Hat Fair street entertainment event in Winchester and was a chorister at the city’s cathedral for five years
“I wouldn’t say I’m particularly well known in Winchester – but that may be a bit different now,” he said.
He explained he developed his act combining his two passions of music and magic.
“I always saw similarities between both – you need a similar mindset, willing to practise a lot and have lots of finger dexterity.
“I tried to create an act that was true and authentic to myself and what I love,” he said.
Bookies have slashed the odds on Rafferty winning the current series of Britain’s Got Talent, should he get through the live semi-final shows.
Victory would come with a cash prize of £250,000 and the chance to perform in front of King Charles and Queen Camilla at the Royal Variety Performance.