Simon Cowell has signed ABBA's Benny Andersson and Bjorn Ulvaeus for 'The X Factor'.

ABBA

ABBA

The music legends will join the reality TV show for the 'Mamma Mia' inspired week and they have agreed to work with the contestants, while Bjorn will also perform.

A source told the Daily Star: "Abba are one of the world's greatest bands and it will certainly give the show a big lift having Benny and Bjorn on board."

Meanwhile, Simon recently revealed that 'The X Factor' and 'Britain's Got Talent' will continue until 2020 after he signed a new deal with ITV.

He said: "We've just been offered an extension on both shows because of the 16 to 34-year-old audience. We could probably do three years or five years. It makes a lot of money.

"We got to a point years ago where we were able to compete with Strictly because there was that huge audience.

"We're losing people now but fortunately the young audience has actually grown this year and all the advertisers and the sponsors want that income on a Saturday."

However, former judge Sharon Osbourne has hit out at Simon, claiming he is to blame for the show's fall in viewers.

She said: "Unfortunately, not out of malice, but I am only saying this because Simon's quote thinks it is funny, that the figures have dropped, and dropped and dropped through the course of the show.

"I am not saying it was all me at all, but (it's because of) his decision to change the show again and again and again."