The former Spice Girls star is no stranger to the panel of the ITV talent show, having been a judge on the 2014 series, but she missed the final of that year's show due to a mystery illness.
However, after reconnecting with Simon Cowell through her work on U.S. reality show America's Got Talent, Mel was apparently the music mogul's first choice to stand in for Nicole as the ex Pussycat Dolls singer had another commitment.
"Mel’s coming in as a guest judge to cover Nicole because she isn’t able to make the first day of filming," a show source told The Sun newspaper.
"This is a diary clash that Nicole had booked in before she agreed to do X Factor and couldn’t change. Mel has been working with Simon as a judge on America’s Got Talent so was available to cover."
Mel's quick wit and often sharp comments have made her a perfect choice for a talent show judge. And Simon is said to be hopeful that she will unleash her inner Scary Spice for the day of judging.
"Simon also knows she’ll come in and take no prisoners so is the perfect temporary replacement for the day," the source added.
This year's series is already shaping up to be one of the harshest so far, following the return of Sharon Osbourne to the panel.
Both Sharon and Louis Walsh are back to search for the country's hottest new stars, but the rock matriarch is said to have caused more than a few tears with her judgements.
"Sharon’s showing no mercy this year. She’s had contestants, who have queued up for 16 hours to audition, in pieces," a source told The Sun on Thursday (16Jun16). "Some were left so distraught by her comments they refused to do interviews afterwards.
"She even described one as looking ‘like a little hooker’. It’s safe to say the b***h is back."