Published Saturday, 20 June 2009
Organisers confirmed that Boyle, 48, would miss Saturday afternoon and evening shows in Nottingham to take a "rest day" but is still expected to perform in London on Sunday.
Cowell admitted: "Looking back on it all, it has become clear to me that we didn't handle the situation with Susan as well as we could have.
"Yet, to be honest, I don't know that I could have done it any differently."
He told the Daily Mail he met Boyle's family last week and asked their opinion about whether she should have been allowed to continue competing once it became clear that she was finding it stressful.
He said they had all agreed with the decision to let her carry on, saying she had always wanted to sing.
Cowell said he had not expected Boyle to become "the most famous woman in the world" when she auditioned.
She had come over "well but not sensationally", he said, although footage of her singing - and the surprised faces of the judges and audience - became an internet hit and won fans including Elaine Paige and Demi Moore.
Cowell said Boyle "seemed fine with all the attention" and told him she was having the time of her life.
The production team raised concerns as the final approached and Cowell said it became clear that Boyle was finding the experience "difficult to cope with" although he added that she was no more nervous before the final than Paul Potts was before his win two years ago.
When dance group Diversity was announced as the winner, Cowell said he looked at Boyle's face and realised she did not know "how to deal with not winning".
Later that night Boyle was taken to the Priory clinic. One of the show's judges, Piers Morgan, said she was emotionally drained and exhausted.
Boyle, from Blackburn, West Lothian, later said she felt able to join the show's live tour but the singer has pulled out of dates in Manchester, Liverpool and Cardiff.