X Factor's Leon Jackson duets with Michael Buble at Wembley

Michael Bublé made an X Factor contestant’s jaw drop last night when he invited him on stage to perform to a packed Wembley Arena.

Leon Jackson, a Scottish shop assistant who only began singing in January, belted out Bublé’s hit Home in front of 12,000 fans last night.

He said: "That's the pinnacle for me man. I'd never rehearsed it with him, I never had a sound check, I just went up and winged it and it was beautiful man, a dream come true and when I came off I was wee bit emotional at the end."

The surprise duet came after the remaining four X Factor contestants had a master class with the Canadian jazz singer, who is due to perform on the ITV1 talent show this weekend.

Speaking at a press conference, Jackson, who judges have compared to Bublé throughout the series, said he wasn't nervous despite his lack of preparation: "I think it was because I knew I wasn't getting judged and I could just go up and have fun."

A star-struck Jackson, who names Bublé as one of his foremost influences, was also invited backstage to meet the 32-year-old’s family and his girlfriend, British actress Emily Blunt.

"It's just incredible because he's sang duets with all his idols like Tony Bennett, and I've grown up in the last few years listening to Michael Bublé and I got to sing with him. I just can't explain it."

Jackson entered The X Factor in the hopes of giving his mother a better life. A single parent, she has struggled financially while bringing up her only child.

The teenager, from West Lothian, began singing earlier this year when his mother bought him an iPod and he started recording his voice. His friends were impressed so he entered the X Factor.

Mentored by judge Dannii Minogue, Jackson has survived seven departures to make the show’s semi-finals this weekend.

He is up against brother and sister duo Same Difference, school dinner lady Niki Evans, and Welsh opera singer Rhydian Roberts. Roberts is the bookmaker’s favourite, but Jackson is a close second.

The winner, announced on December 15, will secure a £1 million recording contract, and will release a version of the Mariah Carey song When You Believe, in time to compete for the Christmas No 1 spot.