The nation's favourite singing competition heads into the semi-finals tonight, where the final four become three.Dermot O'Leary leads the proceedings, while judges and mentors Louis Walsh, Sharon Osbourne, Nicole Scherzinger and Simon Cowell take their seats behind the judges' desk to battle it out with their contestants.Louis has the Groups, Nicole the Boys, Simon the Girls and Sharon the Overs, with drama and disagreements, conflict is sure to follow….Sunday's show will see the next heart-breaking elimination, as Dermot O'Leary, tells the remaining acts who has scored the lowest number of votes and who will be going through to next weekend's final. There will be a nail-biting sing-off before the next contestant leaves the competition.Throughout the Sunday live shows an outstanding line-up of guest stars will perform.