The Australian singers, who rarely collaborate musically, have recorded a festive dance track called 100 Degrees for Kylie's new Christmas album, and they performed the song together for the show's grand finale.

Kylie and Dannii, who is a judge on the TV talent series, wore coordinated disco dresses, with the Spinning Around star in pink and her sister in blue, to perform a song and dance routine, which began at the top of a tall staircase.

"We have been very excited and a bit nervous because it was a very special moment for us," Kylie said after the performance. "It was amazing, thanks for the opportunity... The thing I love about Christmas is family and our mum and dad are in the audience tonight."

The Minogues last performed on TV together in 1986, when they sang Sisters Are Doin' It For Themselves during an appearance on Australian variety TV show Young Talent Time.

They wore matching sequinned dresses teamed with voluminous hair, and Kylie recently admitted they would be ditching the retro looks for The X Factor performance.

"We're not going to be able to give nearly as good hair this time around," Kylie told earlier this month (Nov15). "Or outfits, or anything like that. We literally can't beat that. So we can only aim to honour it."

Kylie shared a video of the duo singing 100 Degrees into the camera during a rehearsal on The X Factor stage. In the caption, she wrote, "Thank SO much to my lil Sis @danniiminogue for #100degrees .... Love you!!!!!"

Dannii also posted a video of the siblings running through their routine backstage.

She previously revealed they deliberately turned down offers to appear together so they could establish themselves individually, saying, "Early on it was important to separate ourselves... Even now we save (duets) for something that feels right or special."

None of Dannii's The X Factor acts made it to the final. Chris Isaak's contestant Cyrus Villanueva was crowned the winner.