For the first time ever, judges Gary Barlow, Sharon Osbourne, Louis Walsh and Nicole Scherzinger were handed their categories before Boot Camp started, adding an extra dimension to the team rivalry for the show's 10th series.
In a similar fashion to BBC One's The Voice UK, the judges then had to pick the acts to join their team immediately after their performances.
Each judge could only take six acts through to Judges' Houses, so the fate of acts lay solely in the hands of one individual judge.
The judges were allowed to swap out acts that they had picked for their Top 6 if someone impressed them more later on, but having to kick quality acts out of their teams generated an incredible amount of tension and tears for the panel.
Tweeting about X Factor over the weekend, Barlow said: "That was the most incredible and exciting X Factor session EVER!"
X Factor returns to ITV later this month.
Watch the trailer for series 10 of X Factor: