Princess Diana‘s intimate love letters to James Hewitt are reportedly set to go on sale in the United States for about $1million, sparking fears they will be made public.

Former Household Cavalry officer Mr Hewitt, who had a five-year affair with the-then Princess of Wales between 1986 and 1991, kept 64 letters she wrote to him.

A US auction house has now reportedly lined up a rich collector to buy the notes, priced at up to $1million, or £780,000 – in what has been called the ‘final insult’ to the memory of the late princess, killed in a car crash in August 1997.

Mr Hewitt, 65, is said to have previously offered the letters – penned between 1989 and 1991 – as collateral for a £500,000 loan.

Intermediaries acting on his behalf contacted London auction house Bonhams last October with a view to selling the collection, the Sun on Sunday reported today.

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Diana, Princess of Wales (pictured leaving the studios of the English National Ballet in February 1996), had an affair with James Hewitt between 1986 and 1991

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Former Household Cavalary officer James Hewitt kept 66 letters Diana wrote to him

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Reports suggest intermediaries for him have been contacting auction firms about the notes

Bonhams declined to sell them and recommended looking for a buyer across the Atlantic – and US auction house Heritage was then contacted.

The company based in Dallas, Texas, describes itself as the ‘world’s largest collectibles auctioneer’.

Ingrid Seward, author of royal book My Mother and I, said: ‘James Hewitt has betrayed Diana in so many ways so this is just the final insult.

‘I presume Hewitt desperately needs the money and he sees the value in these letters.

‘Diana was a prolific letter writer but none of this intimate nature – it is unthinkable these notes for such a sensitive time in her life could become public.’

Diana confirmed the affair with Mr Hewitt during her now-infamous Panorama interview in 1995 with disgraced journalist Martin Bashir.

She said at the time: ‘Yes, I adored him. Yes I was in love with him. But I was very let down.’

Mr Hewitt had been a young Household Cavalry officer at the time and served in the first Gulf war, commanding a tank squadron.

A now-iconic photo, taken during their secret relationship, shows Diana presenting the Captain and Subalterns Cup to Mr Hewitt after he led his Army polo team to glory at Tidworth, Wiltshire, in 1989.

After leaving the Army in 1994, he caused controversy after collaborating with Anna Pasternak, author of Princess In Love, and was reputedly paid £300,000 for sharing details of his relationship with Diana.

Less than a decade later he said he was willing to sell Diana’s letters.

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A 1989 photo shows Diana presenting the Captain and Subalterns Cup to Mr Hewitt after he led his Army polo team to glory at Tidworth, Wiltshire – their affair was ongoing at the time

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Diana confirmed her affair with Mr Hewitt during her 1995 interview with BBC1’s Panorama

During an appearance last week on the American television chat show Larry King Live in 2003, Mr Hewitt claimed the letters deserved a wider circulation because they were ‘important historical documents’.

He indicated that he would be prepared to accept an offer of £10million and there were suggestions at the time Prince William was considering buying them.

But accusations of betraying her followed and the letters remain unsold.

Today’s report says experts at Bonhams valued the collection of letters at between $400,000 (£311,000) and $600,000 (£466,000).

In an email, the firm reportedly told Mr Hewitt’s intermediaries: ‘We believe that open market auction would almost certainly be the best way to achieve the best price.

‘We would recommend sale in the US because there do seem to be more potential buyers at this level there, and because the sale is likely to be less contentious than in the UK.’

An email sent in late January by a leading figure at Heritage was quoted as saying: ‘After much discussion, it was decided that the best way forward to proceed was to work with a likely potential buyer they already have in mind for a private sale.

‘They (the Heritage partners) feel this would remove the letters from appearing at public auction for a long time and remove us from any negative fall-out.’

There was also discussion of arrangements for ‘the material to be fully insured at $1million’.

A spokesman for Mr Hewitt told The Sun on Sunday: ‘Heritage Auctions were approached on behalf of a representative of James Hewitt solely to value and authenticate the letters for personal reasons and insurance purposes.

‘He has no intention to sell and is not soliciting offers to buy.’

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A spokesperson for James Hewitt has said he was merely having the letters valued and has ‘no intention to sell’

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Mr Hewitt was reputedly paid £300,000 for sharing details of his relationship with Diana for Anna Pasternak’s 1994 book Princess In Love

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Mr Hewitt, pictured here at Chagstock Music Festival in Devon in July 2018, previously commanded a tank squadron in Iraq during the first Gulf War

Heritage Auctions’ executive vice-president Joe Maddalena told the Sun on Sunday: ‘We can’t comment, I can’t comment. I really don’t know what you’re talking about. I can’t comment on that. No comment.’

The Daily Mail revealed in 2021 that Mr Hewitt was now living with his widowed mother in the Devon village of Farringdon, working as a £4,000-a-year gardener at her block of flats.

The following year he set up a not-for-profit to help vulnerable people escape from war-torn Ukraine, alongside the son of a decorated British commander who founded a similar fund in Afghanistan.

In recent years Mr Hewitt has suffered both a heart attack and a stroke yet in December 2022 it was revealed he was also driving thousands of miles across war-torn Ukraine to rescue innocent civilians left by Russia’s invasion.