Dermot, who formerly hosted The X Factor for eight years, couldn't resist making a few digs at the show as he presented the National Television Awards in London last week.
His comments didn't go unnoticed, though, and Dermot's old boss Simon has hit back at the 42-year-old, claiming he'll wish he never said them.
Dermot had opened the live awards show, telling the audience and viewers at home: "I've still got this job for now."
And, after Strictly Come Dancing beat The X Factor to win the award for Most Popular Talent Show, Dermot teased it was his "new favourite show."
As Britain's Got Talent films its tenth series, Simon spoke out about Dermot mocking the X Factor at the latest round of auditions.
He told Sunday People: "He's got the NTA job, yeah, for once a year. That's a big move."
"You say these things, trying to be a bit funny on the night, and then you go off and think 'I wish I didn't say that'... That might have been one of those occasions," Simon hit back.
Dermot formally announced he was stepping down from hosting The X Factor in April last year.
He had said at the time: "After eight wonderful years on @TheXFactor it's time for me to move on. I'd like to thank ITV, Simon, The X Factor family and particularly the viewers, all of whom have been a big part of my life for so long."
"I'd like to wish the team all the best for the future, especially whoever takes over from me," he continued. "You're about to be the conductor on the most brilliant, runaway train in showbiz. Good luck you'll love it."
Dermot was replaced by Caroline Flack and Olly Murs and the pair became the first ever duo to hos the talent competition.
Last year's series was won by 18-year-old Louisa Johnson and her mentor Rita Ora. She beat Cheryl Fernandez-Versini's act Reggie 'N' Bollie.
However, it was recently revealed Reggie 'N' Bollie have officially now been signed to Syco Music.
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