The Cowell family have been left devastated, after Julie Cowell passed away on Sunday.
A spokesman for Mr Cowell's family said: 'Today our beloved mum Julie passed away. Anyone who had met her would know what a truly special and kind lady she was.
'We are heartbroken and will miss her terribly, but she is now at peace.'
Cowell's brother Tony paid tribute to their mum, adding: 'Very sad night tonight. We will all miss Mum so very much. She was the heart and soul of our family.’
And a source close to Simon told The Sun:
'Simon is absolutely devastated. His mum was the most beloved person in his life and they were incredibly close.
'But at least she got to see him settle down and start a family which was one of the great wishes of her life. Julie had been unwell for some time and she was in a home. But Simon and his brothers were in constant contact with her and the family remained very close.
'They had been paying regular visits to her bedside and it's been a God send that Simon hadn't had to do too much work in the US over the last year. He's completely heartbroken.’
The first auditions for the new look show- expected to be attended by Cowell and fellow judges Rita Ora and Cheryl Fernandez-Versini, as well as new presenters Olly Murs and Caroline Flack- were due to be held in Manchester today, but have been cancelled until further notice.
A Syco spokesperson confirmed:
'They were due to start today and carry on into Tuesday and Wednesday. Today's have been cancelled and we have not made any decisions beyond that.'
Mrs Cowell was married to EMI music executive Eric, who died aged 81 in 1999.
Our thoughts are with the Cowell family during this sad time.