Nicole Scherzinger Finally Performing on 'The Masked Singer' in Duet

The Pussycat Doll is taking the stage for the first time on "The Masked Singer" ... Nicole Scherzinger is getting out from behind her judge's table and grabbing the mic.

Production sources tell TMZ ... Nicole will perform on the FOX singing competition show after 6 seasons of fans begging to see her show off her pipes.

It sounds like this will be a duet ... we're told Nicole will join the stage with the Queen of Hearts.

While the performance is a long time coming, our sources say it wasn't exactly easy to pull off.

We're told Nicole wanted to make her debut extra special -- ya can't blame her after 6 seasons sitting back and judging everyone else -- so she had 3 outfits to pick from and did 3 wardrobe changes during rehearsals, asking production to rehearse the song 3 times before settling on her look.