Justin Biber

Does The X Factor have Bieber fever?

It appears so.  Justin Bieber joined judge L.A. Reid as a celebrity mentor for his over-25 group of contestants this week, JustJared.com reports.

"Long day but great day," Bieber tweeted Monday. "@LA_Reid @ScooterBraun just like old times!"

Sneak Peek: Simon Cowell, L.A. Reid, Britney Spears and Demi Lovato discuss The X Factor 2.0

Nick Jonas is reportedly the celebrity mentor teaming up with Demi Lovato. There's no word on who will be partnering with Britney Spears or Simon Cowell.

The X Factor kicks off its second season on Wednesday, Sept. 12 at 8/7c on Fox.