The X Factor USA finalist duetted with Morissette on Wednesday night (December 21)'s broadcast and Simon Cowell observed that he thought Krajcik was "intimidated" by the star.
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Krajcik told the official X Factor USA website: "When he said, 'You were a little intimidated', well, duh! He was right. I was."
Adding that he became confused when he tried to leave the stage with Morissette after the song, he explained: "I thought we were leaving. I weirded it out. She's probably like, 'What was that?'
"I didn't know what to do because it was such a big moment for me. I was nervous. I never get nervous, but I was because she's so prolifically amazing!"
© Fox / Ray Mickshaw
Krajcik described his duet song 'Uninvited' as "a pain-filled love song. I love songs like that.
"Man, she can sing. I don't even know what to say."
Krajcik's fellow finalists Chris Rene and Melanie Amaro duetted with Avril Lavigne and R Kelly respectively.
The X Factor grand final airs tonight at 8/7c on Fox in the US and at 8pm on ITV2 in the UK.
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Watch Josh Krajcik perform his $5 million song - 'At Last' by Etta James - below:
