Kelly and Paulina will replace Britney Spears and record producer Antonio LA Reid, for the show's third season.
It's a reunion for Kelly and Simon, although American audiences might not know that Kelly was a judge for a season on the UK X Factor.
After the news was announced, Paulina Rubio told Cowell to "be careful what you wish for", adding that she wondered if the notoriously cranky judge would be ready to handle her.
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