X Factor judge Sharon Osbourne has revealed her stomach would be "knotted with anxiety" at the prospect of sitting next to former panellist Dannii Minogue during her previous stint on the ITV talent show.
In Osbourne's new autobiography, being serialised by The Sun, she said the situation between her and the Australian singer - who it later transpired had been having an affair with Cowell - became "unbelievably bad".
Osbourne said of Minogue: "The antics behind the screen had gone up a gear with her sticking her tongue in Simon's ear and giggling like a bloody teenager as Louis Walsh and I stood there like a couple of gooseberries.
"For me it made her so unbearable to work with that I just couldn't take it. It was horrible. My stomach knotted with anxiety about it and as each show loomed I would wake up and think 'Oh God, I have to spend the day sitting alongside her again'.
"During filming it was obvious to me that there was some sort of relationship going on between them. And the more it progressed, the worse it became between her and me. It was unbelievably bad."
X Factor host Dermot O'Leary has praised the impact of Sharon Osbourne on the new series, saying she has brought the best out of the other judges.
He told ITV's Daybreak: "She has brought Louis back into prominence, it's almost like he is an old sheepdog who has just woken up by the fire.
"Gary (Barlow) has a great sense of humour, she brings that out in Gary and her and Nicole are close."
He added that the show had a more "nostaligic feel" this year and that is was much "warmer" than previous series.
The show starts on Saturday, check out the latest on the X Factor website.
Sharon Osbourne has spoken about how thrilling it has been for the X Factor to return to the traditional closed auditions. This year hopefuls sang directly in front of the four judges in a small room with no audience.
As the judges prepare for the official launch of this year's competition Sharon told Daybreak: "There is nowhere for these contestants to go, once they're there in that small room with us, it's so intimidating - that's what's so fabulous about it."
See the X Factor website for the latest news.
X Factor finalist Jahmene Douglas believes things could "get crazy" on the show this year, with the return of Sharon Osbourne.Read the full story ›
O'Leary promised that Osbourne, who is replacing singer Tulisa, would bring a "kind of anarchy" to the show.
The judges - who also include Gary Barlow, Nicole Scherzinger and Louis Walsh - described what they were looking for in this year's contest.
The X Factor judges – including comeback judge Sharon Osbourne – are back together ahead of the first filmed auditions of the new series.
Osbourne, who was on the show from 2004 to 2007 and replaces Tulisa Contostavlos, will feature alongside Louis Walsh, Nicole Scherzinger and Gary Barlow.
Although preliminary auditions have already taken place, the judges start their first day on the programme today.
Original X Factor judge Sharon Osborne is to return to the show for its 10th anniversary.Read the full story ›
The Black Sabbath front man Ozzy Osbourne has confirmed that he is not divorcing his wife Sharon following reports that the couple were living apart.
The British singer confirmed on his Facebook page that over the past year he has been "drinking and taking drugs". He apologised to his family and said that he was pleased to say he "has been sober for the past 44 days".
His son Jack Osbourne also rubbished reports that his parents were separating. Writing on his Twitter account he said "Last time I check (sic) a lot of British news papers weren't amazing sources of accurate information. Moving on..."