Rihanna to guest judge on 'The X Factor'

"The X Factor," FOX's new singing competition, is pulling out all the stops to ensure its success. R&B superstar Rihanna is aboard the show as a guest judge according to TMZ.

This will be a bit of a reunion for the "Umbrella" singer and "L.A." Reid, already a judge on the series. Music mogul Reid signed Rihanna back in 2005. She's since gone on to have five multi-platinum albums and now has a burgeoning movie career with her role in "Battleship."

The singer previously made an appearance on the U.K. version of the Simon Cowell-produced reality show.

This news comes as the show's marketing machine ramps up, including the eight-minute ad the show released on Sunday (Sept. 11).

The FOX series bows Sept. 21 at 8 p.m. ET.