From the Sun:
"it had 'greatly angered' Princess Diana.
He said: 'A simple comparison of dates proves it is impossible for Hewitt to be Harry’s father. Only once did I ever discuss it with her, and Diana was in tears about it.'
'Harry was born on September 15, 1984, which means he was conceived around Christmas 1983, when his brother, William, was 18 months old.'
'Diana did not meet James Hewitt until the summer of 1986.'
'The red hair that gossips so love to cite as ‘proof’ is, of course, a Spencer trait, as anyone who has ever seen a photograph of Diana’s sister, Jane, for example, as a young woman will be able to testify.'"
Testimony from a chauffeur of Diana's who talked about the affair from around 1989 to 1994.