London, November 9 : Mariah Carey, who's known for her astounding eight-octave vocal range, left the star-struck 'X-Factor' contestants gasping for air when they met up with the super-singing sensation hours before the show.
The contestants, who received a class from the world's biggest-selling female artist as they prepared to perform one of her hits, were said to have had the frozen feet.
"The contestants have been a bit like, 'Wow, it's actually Mariah Carey'," the Daily Star quoted vocal coach Yvie Burnett as telling them.
"There's nothing harder than singing a Mariah song in front of Mariah.
"Unless you are Leona Lewis you are not going to be able to do it as well and I think the finalists were all terrified," Burnett added.
The effect of the superstar's appearance is said to have caused alleged worries to judge Simon Cowell who is left to imagine 'problems' that are bound to come up when Britney Spears and Beyonc make guest appearances later in the series.