The star has been left “heartbroken”, after the 89-year-old passed away on Sunday (5 July), after suffering a stroke.
Simon’s close friend Sinitta and new ‘X Factor’ host Olly Murs have led the tributes to Julie on Twitter, after it was announced that auditions for the show had also been postponed as a result of Simon’s bereavement.
Dearest beloved friend died today, so lost without her, but the finest, happiest memories and lessons remain of my Beautiful Mother-Look— Sinitta 19 (@sinittaofficial) July 5, 2015
Thinking of you @SimonCowell love you lots X— Stacey Solomon (@StaceySolomon) July 6, 2015
— Matt Cardle (@mattcardle) July 6, 2015
@SimonCowell so sorry to hear your mum has sadly passed away x heaven has gained another angel x ❤️— Sam Bailey Official (@SamBaileyREAL) July 5, 2015
Thinking of my old mentor and friend @SimonCowell on this sad time...I love you Simon xx— STEVI RITCHIE (@THESTEVIRITCHIE) July 5, 2015
I would just like to take a moment to send my love to @SimonCowell, so sorry to hear the news. They always say heaven needs its Angels.— Lloyd Daniels (@LloydDanielsUK) July 5, 2015
all of our thoughts are with @SimonCowell, so sorry to hear about your news, RIP x - jake— Stereo Kicks (@StereoKicks) July 6, 2015
Announcing Julie's death last night, the family said they were heartbroken and would "miss her terribly".
"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," a statement said.
"We would like to thank the media for kindly respecting Julie's privacy throughout and we politely request continued privacy for the entire family at this particularly difficult time."
Julie was the mother of four boys - Nicholas, Simon, Tony and Michael, and step-mother to John and June.
It is currently unknown if ‘X Factor’ auditions will go ahead in Manchester, on Tuesday, as planned.