Bethany Fenton, who had an inoperable brain tumour, was granted her wish to visit his TV studios on Saturday.
She sang Twinkle, Twinkle Little Star to the judge in his dressing room after afternoon rehearsals.
But she became poorly on Monday and, in the early hours of yesterday, she was taken to the John Radcliffe Hospital in Oxford where she died.
Bethany’s dad Sean told The Sun how she turned to him one day and said:
“Daddy, I’d love to meet Simon Cowell.”
“It broke my heart when she said that.
“We appealed to the programme and told them our girl was the bravest child you could ever meet.
“They came back with the response that they would be delighted to welcome her to the show.
“We are now doing everything we can to arrange for Bethany to sing Simon her favourite song, Twinkle Twinkle Little Star.
“She loves all the kids on the programme and just wishes she was one of them.”
A friend of the family then wrote to the BGT team saying:
“Bethany constantly tells me that she’d love to see Britain’s Got Talent and would like to sing Twinkle Twinkle Little Star to Simon.
“I appreciate you have many such requests and that they are all heartbreaking. In Bethany’s case her life expectancy could be just months or a year or two. There is no cure.
“Bethany has no idea that I have applied and her parents understand you have the most difficult job.”
A producer from the show replied:
“Bethany sounds like an amazing little girl.
“We would love to invite Bethany and her family to the studio in Wembley. All being well, she will get the opportunity to sing to him.”
It is not yet clear if Bethany will be appearing on the show or not, but one things for sure, she will be treated like royalty while she’s there. Simon Cowell is well known for his generousity.