Simon Cowell has paid off a US couple's mortgage, to help them look after their seriously ill daughter.
Cowell told Oprah he had only just realised how good it was to give
He promised to be three-year-old Madelaine Stoen's "guardian angel" after being shown footage of the family on Oprah Winfrey's US TV chat show.
Madelaine's parents were struggling to pay their £80,000 debt because they had to travel more than 100 miles every day for Madelaine's cancer treatment.
Cowell said: "I never knew doing good could feel so good."
Madelaine, from Claremont, Minnesota, was diagnosed with an aggressive form of cancer, alveolar rhabdomyosarcoma.
She has already started losing her hair.
'It's taken 48 years'
After seeing a video of the family, The X Factor judge, dubbed TV's 'Mr Nasty', said: "I didn't know what to do in this situation, other than to do something which I hope will help your situation.
"I know that you're having problems with your mortgage. As of this afternoon your mortgage has been paid off."
After writing the cheque, Cowell told Oprah he had only just realised how good it was to give, and added: "It's taken me 48 years. I credit you with this."
The multi-millionaire judge had appeared on the chat show to promote X Factor winner Leona Lewis in America.
Cowell is also known in the US for appearing on American Idol. He recently came third in a Forbes.com rich list of the best paid TV stars, earning an estimated $45m (£22m) last year.