The 18-year-old made it to bootcamp after impressing Gary Barlow and Kelly Rowland with a cover of True Colours at her audition in Cardiff.
But being snubbed, the teenager says she left more determined than ever to impress, and couldn't wait to sing for Simon Cowell this year on Britain's Got Talent.
Welsh singer Chelsea wowed the judges with her take on Prince classic Purple Rain to win a place in the next round on Saturday night.
Speaking to DigitalSpy, Chelsea said: "When I didn't get any further on The X Factor it made me more determined to come back.
"I've always wanted for Simon to hear me, so when I heard that he was judging Britain's Got Talent I really wanted to come back and audition.
"He's the main man really, I really wanted him to hear me. He were so lovely and I couldn't have wished for better comments from him."
The youngster also teased her future performances on the show, saying: "I don't know if I'm going to do a difficult song but I'm definitely going to change something up."
Britain's Got Talent 2012 continues this Saturday on ITV1.