Jackie Kennedy with John F Kennedy shortly after the announcement of their engagement in 1953.

Written in Jackie Kennedy’s neat and feminine hand, the letters remained hidden for more than four decades.

But now the stash of secret correspondence between the widowed Mrs Kennedy and a British aristocrat have shed light on her grief and passion following the assassination of her husband, President John Kennedy.

Five years after the 1963 shooting, Mrs Kennedy went on to marry the belligerent Aristotle Onassis – baffling the former First Lady’s friends and admirers.

And it seems that David Ormsby Gore, the 5th Lord Harlech, who desperately wanted her to become his wife, was among those who struggled to understand why she had rejected him in favour of a Greek shipping magnate 23 years her senior.

In the never-before-seen correspondence, Jackie explains why she had to move away from the US and ‘my world of past and pain’ to start afresh.

Writing from Onassis’s yacht, she told the peer: ‘You and I have shared so many lives and deaths and hopes and pain – we will share them forever and be forever bound together by them… If ever I can find some healing and some comfort – it has to be with someone who is not a part of all my world of past and pain.’

Lord Harlech was a childhood friend of JFK. He went on to become British ambassador to Washington during JFK’s presidency. After the President’s murder in Dallas in November 1963, Lord Harlech and Jackie continued to be friends and became even closer when the peer’s wife, Sissy, was killed in a car accident four years later.

In an earlier letter, Mrs Kennedy, responding to Lord Harlech’s proposal of marriage, tried to explain why they could not be man and wife. Writing in February 1968 she said: ‘We have known so much & shared & lost so much together – Even if it isn’t the way you wish now – I hope that bond of love and pain will never be cut… You are like my beloved, beloved brother – and mentor.’

In another, following his wife’s death, she wrote about feeling desperate to heal the aristocrat’s grief, saying: ‘I would do anything to take that anguish from you – you want to patch the wounds and match the loose pairs – but you can’t because your life won’t turn out that way.’

In the months following the accident the two spent more and more time together, often on private holidays, and in February 1968 the aristocrat proposed.

One of the documents appears to be an early attempt, by a wounded Lord Harlech, to write a response to her rejection. He said: ‘All the pathetic plans I had brought with me… all had become irrelevant trash to be thrown away.’

The letters – 18 handwritten and one typed – were locked away in two official red Government despatch boxes at Lord Harlech’s family home, in Glyn Cywarch, Gwynedd, north Wales, following his death in 1985.

Other papers in the cache, which could be worth up to £150,000, include letters from President Kennedy and from Prime Ministers Harold Macmillan, Sir Alec Douglas-Home and Harold Wilson.

They are part of a treasure trove of art, antiques and memorabilia being sold by his grandson Jasset, 7th Lord Harlech, to pay for the restoration of the family seat.

Matthew Haley, of Bonham’s, which is auctioning the papers, said: ‘For decades, biographers have speculated on the precise relationship between Jackie Kennedy and David Ormsby Gore. These letters now show without doubt how close they came to marriage and why Jackie decided to marry Onassis instead.’

Her letter to Lord Harlech (from Aristotle Onassis’s yacht)

If ever I can find some healing ... it has to be with someone who is not a part of all my world of past and pain

Daily Mail