The trio are made up of SeSe, originally from group Dynamix, and soloists Jeanette and Rielle.
Groups' mentor Gary put the three girls together at bootcamp after Nicole Scherzinger had previously given them nos.
They blew the judges away in their audition, after only being together for 10 hours and singing their rendition of We Found Love by Rhianna.
"When myself, Jeanette and Rielle were called back to the room, we didn’t know what was happening," SeSe recited this week. "We were all just very sad as we’d all got a ‘no’ from the Judges. But then Gary appeared and told us his plan to put us together, and we all screamed.
“We had been sitting there for a while and ended up talking a lot and even singing songs together. I remember even saying, ‘Guys, we look like a group’. We automatically seemed to take our own pitches during the harmonies and we just matched each other when we looked in the mirror."
But the girls have competition from rival girl group Xyra, with just three spots in the live shows.
Gary said of the four piece at bootcamp: "They completely nailed it. I am big on vocals and I like the vocals to be strong and I just thought, they deserve a place.”
He added: "It’s really strong category, I knew it all along! It’s the strongest category I’ve had since Ive been on the X Factor."