Prince William talked Diana out of Martin Bashir book deal calling him 'sly creep'

Prince William reportedly talked Diana out of a book with Martin Bashir calling him a 'sly creep'.

Close friend of the princess, Hasnat Khan, was reportedly the first to warn Diana to stay clear of Bashir - but Prince William is said to have frankly have told her “he’s a sly creep, Mummy”.’

Diana eventually told Bashir she wanted to back out of the book project, claiming that divorce terms would not allow her to make commercial arrangements.

Bashir however is said to have begged Diana to ask Prince Charles for permission to go ahead - but she refused, reports the Mail.

Prince William was left 'devastated' at 13 when he watched his mum's Panorama interview as a schoolboy, a royal expert has claimed.

William was said to have helped talk his mother out of a book project with Bashir (Getty Images)

Diana is said to have later regretted taking part in the Bashir interview (Tim Graham Photo Library via Getty Images)

It was broadcast a year before Diana and Prince Charles were formally divorced in 1996, though they had separated in 1992.

In the sensational interview in November 1995 Diana admitted committing adultery and being in love with James Hewitt.

She also uttered the infamous line “there were three of us in the marriage, so it was a bit crowded” in relation to her husband’s affair with his now wife Camilla.

But according to a friend, Princess Diana was also said to have regretted ever taking part in the now-infamous interview on the BBC programme.

Princess of Wales, during her interview with Martin Bashir for the BBC (PA)

Diana with sons Harry and William in May 1995 (Getty Images)

Prince William watched the interview in a master's study at Eton and according to royal biographer Penny Junor, the young Prince was left feeling devastated.

She told The Times: "He was deeply upset, as any child, watching one parent assassinate the integrity of the other, let alone talk about their infidelity, would be.”

The publication reports that 'what Diana had not considered was the effect the interview would have on her children.'

Following Diana's death her friend Rosa Monckton was reported to have said that she had regretted what she had done.

She said: “It was born of some basic desire to hurt those who she felt betrayed her. But she also had the ability to admit her mistakes, and she said to me that she regretted doing the programme.

“The sad thing is that it was her only television interview, and it was Diana at her worst.”

The BBC on Thursday made a “full and unconditional apology” for the interview.