Louis Walsh accused Simon Cowell of cheating on last night's 'X Factor'.
The Westlife manager - who returned to the ITV talent show after missing the past three shows due to the tragic death of Boyzone star Stephen Gately - said his fellow judge had bent the rules after giving his contestant Jamie Archer a U2 song to sing on Big Band night.
Talking about Jamie's performance of 'Angel of Harlem' - which was changed on Friday from Elvis Presley's 'If I Can Dream' - Louis said: "I'm a bit confused because the theme is big band and you came out and sang a U2 song. I know your mentor changed your song but I feel it's cheating everyone else. I wouldn't get away with it and neither would the girls - I don't know why Simon does."
Simon - who is mentoring the over 25s - hit back with a quip at Louis' act, John and Edward.
He said: "For Louis to sit there like someone from the council with a rule book saying, 'you can't do this you, can't do that'
"I don't think you're in a position to judge for us about musical taste with the two horrors you've got coming up."
The Irish twins - who have divided the nation - sang a version of Ricky Martin's 'She Bangs', complete with their now trademark energetic dance routines.
Dannii Minogue told them: "I'm really absolutely torn here. The singing is not of the standard that is going to follow Alexandra Burke to win, but it's entertaining."
Cheryl Cole added: "You are two of the nicest kids I've ever met. I think the boos are pantomime. You're fast becoming my guilty pleasure. I can't wait each week to see what you're coming out with."
The next act to leave the competition will be announced in a live show tonight.