Osbourne will host six hopefuls in Los Angeles, alongside veteran popstar - and former guest mentor - Robbie Williams.
Andrea Magee, 28, made her mark by performing an original song with flute when first in front of the judges. At Boot Camp, she took on 'With or Without You' by U2.
Shelley Smith has made it to Boot Camp twice before, but this year the 34-year-old delivery driver broke through to the final six with her performance of 'Respect' by Aretha Franklin.
Prison officer Sam Bailey, 35, impressed the judges with her room performance of 'Listen' by Beyoncé. She then won her place in Los Angeles by singing Emeli Sandé's 'Clown'.
Zoe Devlin, 28, is a former backing vocalist for Alabama 3. After quitting the band several years ago when she found out she was pregnant with 3-year-old daughter Dusty, Zoe returned to the stage and wowed the judges with her version of Joe Cocker's 'You Are So Beautiful'.
The only male to make it through in the over-25s is Joseph Whelan, 27. This was his second time at Boot Camp and, after falling at the last hurdle in 2012, Joseph made it to Judges' Houses by singing 'Iris' by the Goo Goo Dolls.
Lorna Simpson completes Sharon's finalists. The 26-year-old dreams of following in Mariah Carey's footsteps and impressed with performances of Whitney Houston classics 'I Have Nothing' and 'Dance with Somebody'.
The X Factor continues on Saturday, October 5 at 8.20pm on ITV.