Manuel Pons Sanchez performed on the ITV talent show in 2009 despite police looking for him after he attacked a 10-year-old girl.
The wannabe singer wowed the judges with his audition but was hiding a very terrifying secret.
Unknown to judge Simon Cowell, who praised him after his performance, the 46-year-old was being hunted for a series of sexual assaults on a girl when she was aged between six and 10.
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Sanchez, who is from Menorca, made it to boot camp on the show after his audition was a success.
After hearing him sing, Simon said: “Hey, Manuel, we like you. I don’t think anyone’s going to try harder.”
But producers and the judges were completely unaware that he had been reported to Spanish police by his victim’s mother in 2007.
The Spaniard was convicted for beating the young child before assaulting her, leaving her suffering from anxiety and post traumatic stress disorder.
Manuel was jailed for 23 years and six months last August.
The criminal fled Spain, after raping the girl, to Liverpool and worked at Whiston Hospital.
An NHS Trust spokeswoman spoke out after the Spanish authorities failed to notify their British counterparts about Sanchez.
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They said: “We have been assured by Medirest that they complied with all mandatory NHS pre-employment requirements.
“This included an enhanced Disclosure and Barring Service check which did not highlight any issues.”
A spokeswoman said of Pons Sanchez: “Prior to his employment all the relevant background and security checks were taken, including an enhanced DBS check.”
Representatives for The X Factor have not yet commented.