The brothers lost their beloved mum Julie to cancer last week and Tony opened up in his latest Best magazine column about how they're coping.
He said: "I feel for all my family, including Simon, who must live out his grief in the glare of the spotlight. That's not easy but the Simon I know and love will come through. Like mum, he's a fighter – he never gives up."
Tony went on to say that his only wish was Simon's son Eric, 17 months, had been able to spend more time with his grandmother.
"Mum's death has hit us all hard but I know she'd want her boys to move on. I only wish baby Eric could have had more time to get to know how wonderful his grandmother was."
Simon cancelled the start of X Factor auditions following Julie's death and issued a statement saying: "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."
For the full interview with Tony Cowell, pick up this week's Best magazine, on sale now
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