Simon Cowell has paid off the mortgage of the parents of a cancer-stricken girl.The British music mogul - dubbed 'Mr Nasty' for his jibes as a judge on singing contest 'American Idol' - wrote US couple Amy and Randy Stoen a cheque for $162,000 to help them cope with their three-year-old child Madelaine's illness.Simon, who announced his good deed on Oprah Winfrey's new show 'Oprah's Big Give' yesterday (17.03.08), said: "I never knew that doing good could feel so good."It doesn't stop here. If there's any problem, I'm her guardian angel now."In January, Madelaine was diagnosed with alveolar rhabdomyosarcoma, a rare and aggressive form of cancer, after her parents found a cyst inside her nose.The cancer has since spread to the left side of her face, and Amy and Randy have to travel 100 miles to Saint Mary's Hospital in Minnesota each day for Madeleine to receive chemotherapy treatment.It was recently revealed Cowell - who is believed to be worth $200 million - will leave $180 million to charity in his will.

The 48-year-old star, who has no children, will leave the mammoth sum to a selection of organisations helping children and animals.