Former Spice Girl Mel B is The X Factor's Underdog Judge.
Former Spice Girl Mel B is The X Factor's Underdog Judge. Ernesto Casillas

Mel B officially confirmed as X Factor's underdog judge

IN ONE of the worst kept TV secrets of this year, Mel B has been unveiled as The X Factor's Underdog Judge.

The former Spice Girl was confirmed as the reality singing show's fourth judge during tonight's show.

Her existence was kept secret from the other three judges - Guy Sebastian, Iggy Azalea and Adam Lambert - during the filming of auditions but she has long been tipped by industry commentators as the most likely candidate.

Further speculation was fueled late last week when Mel B started following her fellow X Factor judges on social media.

"I'm a fighter, a fierce competitor and love mentoring upcoming artists, so the Underdog Judge role is a perfect fit for me," Mel B said in a statement released by Seven.

"Guy, Iggy and Adam are going to be left with egg on their face."

Mel B is no stranger to The X Factor Australia. She was a member of the judging panel in 2011 and 2012. She attempted to jump to Channel 9's Australia's Got Talent the following year but in a contract dispute Seven prevented her from appearing on AGT.

Instead in 2014 she appeared as a coach on Nine's The Voice Kids and guided Maddison Milewski, who was seen getting through the X Factor auditions last night, to the grand final.

Leading a new category of 'underdog' contestants, Mel B will hand pick artists that current judges will send home in the upcoming three seat challenge round starting on Sunday.

"If Mel B wins the competition with an act I said no to, I'll never forgive myself," Azalea said.

Mel B's Underdog category will take on Lambert's Under 22s, Sebastian's Over 22s and Azalea's Groups.

Her Underdog hopefuls will be revealed during The X Factor's first live show later this month.