Simon Cowell opened up to his biggest career regret on "The Tonight Show" -- and it has nothing to do with his under-performing "The X Factor" in the U.S. According to Cowell, his biggest regret is the Spice Girls. He told Jay Leno that he knew they were going to be big, but he was too late on the deal.

"I offered them a deal, but they didn’t want to sign to me and that kinda hurt at the time," Cowell said. But Posh Spice, Victoria Beckham, tells a different version of the story. When she guest-judged alongside Cowell on "American Idol" in 2009, she said, "He is the only man in the music industry who turned down the Spice Girls - and said we would never work. I like that fact.”

Whether he turned them down, or came too late with his offer, Cowell missed out on one of the biggest-selling, and most popular girl groups of all time. But things are looking up for Cowell. His current girl group, Little Mix, became the first-ever British girl group to debut in the top five of the Billboard charts with their debut album. Spice Girls debuted at number six back in 1997.

Simon Cowell can be seen on "The X Factor," Wednesdays and Thursdays at 8 p.m. EST on Fox. "The Tonight Show with Jay Leno" airs weeknights at 11:35 p.m. EST on NBC.

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  • 'Jimmy Kimmel Live'

    Airs weeknights at 11:35 p.m. ET on ABC.

  • 'The Tonight Show With Jay Leno'

    Airs weeknights at 11:35 p.m. ET on NBC.

  • 'Conan'

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  • 'Chelsea Lately'

    Airs weeknights at 11 p.m. ET on E!

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  • 'Watch What Happens: Live'

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  • 'Totally Biased With W. Kamau Bell'

    Airs Thursdays at 11 p.m. ET on FX.

  • 'BrandX With Russell Brand'

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  • 'The Late Late Show With Craig Ferguson'

    Airs weeknights at 12:35 p.m. ET on CBS.

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    Airs Friday nights at 11 p.m. ET on HBO.

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    Airs weeknights at 1:35 a.m. ET on NBC.