Calum made the final of BGT in 2015 and in 2016 scored a top ten debut with his first single.
The singer, who had been backed by Simon Cowell with a golden buzzer, released his cover of Robyn's Dancing On My Own.
Without the help of major backing, the song took its sweet time to climb the charts but eventually proved even more successful than Robyn's original release of the song which peaked at Number 8 back in 2010.
Leona meanwhile won The X Factor back in 2006 and went on to become one of the show's most successful contestants.
However while she enjoyed much success in the late 00s, Leona's chart career has since declined and she was dropped from her latest label last year.
Her fifth album out in 2015 peaked outside the Top 10 and sold 8,500 copies in its first week.
Now Leona is making a comeback alongside Calum, who is working on his first album.
She appears on his new song You Are The Reason, taken from Calum's debut record Only Human, due out in March.
The single will be out to download now (Friday, February 9).
"To have her on a song that I’ve written myself is a surreal feeling," Calum told The Sun.
You can pre-order his album here.
Meanwhile, Matt also revealed Leona was working on her own music too.
He added: “She is coming back with new music. We’ve talked about writing with each other.
“She’s going to smash it. Her voice is just as strong and beautiful as it was on the first album.”
We can't wait to hear what she comes out with...