Music mogul Simon Cowell has been left devastated after a critically ill child he attempted to save passed away.

The American Idol judge vowed to help 23-month-old Sophie Atay, who was diagnosed with a rare, aggressive cancer known as neuroblastoma, after he became aware of her plight when he signed up as a patron of Children Hospices U.K, a charity which helps sick kids.

He donated his own cash to help raise $800,000 to send Sophie to New York to receive specialist treatment.

But the toddler sadly lost her battle with the disease on Thursday before she could fly to the Big Apple for medical aid.

Cowell says, "It's a tragedy."

Simon Cowell Gallery