Over the past four weeks, we've seen judges Simon Cowell, Nicole Scherzinger, Sharon Osbourne and Louis Walsh travel the country searching for the next big pop superstar.
But tonight the competition really began, as the 124 acts who succeeded at their room auditions checked in to Bootcamp.
Filmed at the SSE Arena in Wembley, Bootcamp saw the contestants compete in two separate rounds. Only those who made it past both got to progress to the Six Chair Challenge.
Wall of Songs/group performances
First, they had to work in groups in a bid to impress the panel - and the 'Wall of Songs' returned to decide who teamed up with who.
As the name suggests, it's literally a wall covered in song titles, printed on cards. Each song appeared on the wall multiple times.
The contestants were let loose all at once, with each aiming to grab the track they wanted to perform. They were then grouped with everyone who chose the same song.
If anyone was unhappy with their choice, or the group they ended up in, they were allowed to trade - as long as they could find someone else willing to swap.
Once the groups were finalised, they had a short time to rehearse before performing on stage, in front of all the other acts. The judges then decided collectively who would proceed to the next round.
Here's a rundown of tonight's group performances...
Group 1: Bruno Mars - 'Locked Out Of Heaven'
Yes: Anthony Russell, Kevin Davy White
No: Rebecca Kelly, Tommy Kendall
Group 2: Marvin Gaye - 'Aint No Mountain High Enough'
Yes: Georgina Panton, Taliah Dalorto, The Cutkelvins
No: Peter Warwick
Group 3: One Direction - 'History'
Yes: Daniel Warwick, Harry Davidson, Scarlett Lee
No: Jack Smith
Group 4: Bruno Mars - '24K Magic'
Yes: Charlie Cammish, New Dynamixx, Rak-su
No: Jack Morgan, Riley Peters
Group 5: Elle King - 'Ex's & Oh's'
Yes: Chloe Rose Moyle, FAE, Holly Tandy, Karen Mullan
Group 6: Clean Bandit feat. Zara Larsson - 'Symphony'
Yes: Aidan Martin, Jodie Woolcott
No: Caroline Widdows, Liia
Group 7: Dead Or Alive - 'You Spin Me Round'
Yes: Russell Jones, Hayley Norton*
No: Descendance, Doctor Woof, Ginny Lemon
*After the result, Simon held family duo Descendance back, and offered daughter Hayley the chance to proceed a solo contestant. Mother Debye agreed to split the group. Therefore, Hayley will now continue on her own, while Debye has been eliminated.
Group 8: Mariah Carey - 'We Belong Together'
Yes: Alisah Bonaobra*, Rai-Elle Williams
No: Natalie Lomax, Gaga Lord
*Alisah was given a 'no' after the group performance, but, desperate to stay in the competition, she sang part of the song a capella before leaving the stage. Based on this, the judges decided to change their mind and give her a 'pass'.
Group 9: Beyoncé - 'Love On Top'
Yes: Deanna, NQ
No: Chelsea, Rebecca Grace
Group 10: James Arthur - 'Say You Won't Let Go'
Yes: Grace Davies, Gregor Coleman, Lloyd Macey, Spencer Sutherland
Next, each act must take to the stage again and perform on their own. However, this time the audience isn't their fellow hopefuls - but a baying mob of thousands of X Factor fans.
Again, the judges deliberate as a group, and if they like what they hear, the act goes through to the Six Chair Challenge.
Tonight we heard four arena auditions - here's how they went…
Matt Linnen (Yes) - Plasterer Matt received mixed feedback at his room audition, with Nicole saying she liked the "texture and tone" of his voice, but struggled to "connect" with him. He got his guitar out again in the arena to perform Beyoncé's 'If I Were A Boy', and the unexpected song choice proved a winner. "I think the public will like him, his personality," commented Sharon. "He's like a guy in a pub that you'd have a drink with."
Shanaya Atkinson-Jones (Yes) - Shanaya has already experienced high praise from the judges, with Simon previously describing her as "everything I hoped we were gonna find this year". The adoptee sang Luther Vandross's 'Dance With My Father' as a tribute to her parents, whom she describes as her "best friends", and the performance reduced Nicole to tears. "I just wanted to say thank you for that," said the ex-Pussycat Doll. "You always give such an honest performance. I feel like whenever you sing you take us somewhere else."
Jodie Woolcott (No) - We hadn't seen Jodie until tonight, as she was cut from the room auditions - but after her unfortunate turn at the arena, we won't be seeing any more of her. Her song choice - Meghan Trainor's self-empowerment anthem 'Me Too' - certainly suggests she's got a pop star attitude, but the judges thought she was a little bit too confident. Nicole reckoned she "took herself too seriously" and Sharon even suggested she came across as "so precocious".
Alisah Bonaobra (Yes) - Having narrowly avoiding the axe in her earlier group performance, Alisah had "a point to prove" (Simon's words) in round two - and prove it she did with a powerful rendition of Wicked track 'Defying Gravity', which earned her a standing ovation from the 4,000-strong Wembley audience. "What happened to you in 24 hours?!" Simon exclaimed. "You were literally lying on the floor crying, and now this!"
Bootcamp continues tomorrow night at the earlier time of 7.30pm on ITV, with more arena auditions.