The music mogul also thanked fans for their support in the message he posted on Twitter.
He said: “My family lost someone very special on Sunday. My Mum. I am overwhelmed with gratitude for all of the kind messages received. Thank you. X”
The tweet comes after Simon cancelled two days of auditions on the new series of ‘The X Factor’.
Simon with his mum Julie, who died on Sunday
The devastated star is set to throw himself back into work today (Wednesday) just three days after Julie died from a stroke at the age of 89.
He will join fellow judges Cheryl Fernandez-Versini, Nick Grimshaw and Rita Ora on the panel for a week of auditions starting in Manchester before moving down to London.
The new 'X Factor' panel
A source told The Mirror: “Simon needs time to get over the death of Julie, it is a huge loss for him and his family.
“But at the same time, he knows how many people are involved in the X Factor and doesn’t like to let people down.
“Julie was a big fan of the show, so it feels right to take some time out and then come back and work on the show later in the week.”
A spokesman for X Factor added: “We can confirm that The X Factor auditions scheduled for tomorrow (Tues) have been cancelled. We will now start auditions in Manchester on Wednesday and Thursday this week."