The 56 year old surprised the mum of a little boy with cancer with a whopping donation, when he phoned her to donate a total of £25,000 for her son's cancer treatment.
Simon, who became a father to son Eric in 2014, says he was touched by Kian Musgrove's story who, at only three year old, has been diagnosed with an aggressive form of childhood cancer for the second time.
His family started campaigning to get £500,000, the money they need to get specialist relapse treatment for Kian's neuroblastoma, either in the US or Germany.
An online campaign to get Simon involved in fundraising the money attracted his attention, which is how he came to know about Kian's story.
Spealing to Chronicle Live, Kian's mum Kat said: 'I can't believe it, I have tears streaming down my face. He just called up and said he wanted to help and said he would drop £25,000 into our fundraising account.'
'I'm still trying to get my head around it all. He was so nice and kind and just said he wanted to do something to help. It was such a lovely surprise which has come at such a difficult time. This means so much.'
Kian's mum also thanked everyone else's support, as many well-wishers have been dedicated to fundraising the money by organising charity events and raffle prizes.
'I want to thank everyone who has donated, everyone has been incredibly kind', she said.
Simon, who, according to Kat, also offered to pay for the flights to the New York clinic, has extended his support for Kian's campaign on social media.
Taking to Twitter, he said: 'Kian Musgrove is a truly brave young boy. I have just spoken to his mum.'
The music mogul then appealed to his fans's generosity, writing: 'Let's help get him to NYC for the life-saving treatment he needs. #CaringForKian #GetKianToSimon'
Kian Musgrove is a trulyÂ brave young boy.Â I have just spoken to his mum.— Simon Cowell (@SimonCowell) February 24, 2016
Little Kian is currently undergoing chemotherapy at Newcastle's Great North Children's Hospital.
He was first diagnosed with stage four neuroblastoma in 2013, and recovered after eight months of intensive treatment.
Sadly, his family found out last December that he would have to battle the illness again.
According to Macmillan Cancer Support, neuroblastoma is the second most common solid tumour in childhood, and most children who get this cancer are younger than five years old.
The disease usually first develops in the adrenal glands but then spreads to other areas like bones, liver and skin.
Get well soon, Kian.