Sir Ranulph Fiennes drew up a secret will at Everest base camp after a major crisis in his marriage, it was claimed last night.

Michael Kobold, a friend of the explorer for 30 years, told The Mail on Sunday that Sir Ranulph wrote the document by hand in his tent the night before an unsuccessful bid to reach Everest's 29,000ft summit.

Sir Ranulph gave the sealed will to Mr Kobold, who still has it, in May 2008 with the instruction to open it in the event of his death.

In an exclusive interview, Mr Kobold, a German watch entrepreneur who lives in Switzerland, said that two months earlier, just before leaving the UK for Nepal, Sir Ranulph decided to divorce his second wife, Louise Millington-Cotes.

Sir Ranulph even asked Mr Kobold to find a law firm and public relations expert to handle the proceedings.

But it is claimed Mrs Millington-Cotes discovered the plan and a 'much deflated' Sir Ranulph changed his mind after she confronted him at their farm on Exmoor, Somerset.

Mr Kobold said last night: 'I don't know what's in the will and I promised Ran I wouldn't open it until he died.

'I get emotional thinking about it because it was a difficult time for all of us. Ran was not happy with the situation.

'I was there when he wrote it longhand. I was there when he signed it. In Ran's mind, this was a very bleak time in his life. Probably the darkest time, up until then, because he felt trapped.'

The extraordinary claim follows a storm of speculation about the whereabouts of the world's greatest living explorer, who was last seen in public two years ago.

Sir Ranulph, 82, who has Parkinson's disease, is said to have been shunted around a succession of care homes in London, Wales and Cheshire by Mrs Millington-Cotes, with his identity concealed under an alias, stopping his friends seeing him.

Mrs Millington-Cotes, a horse trainer from Cheshire, married Sir Ranulph in 2005 following the death of his first wife, Ginny, the previous year.

At one home, in London, she reportedly made visitors sign non-disclosure agreements, and at another, in Wales, where he was registered as Robert Millington, she allegedly gave instructions for him not to socialise with other residents.

Following an outcry from friends, who have called on the police and Office of the Public Guardian to investigate, Sir Ranulph is now believed to be back home at his isolated farm in Shropshire, which is hidden by a 6ft security gate.

Mr Kobold, who is publishing a book on Sir Ranulph's disappearance, stayed with the explorer and his wife for several weeks in 2008 and says he was appalled at the way that Mrs Millington-Cotes treated his friend.

'Louise subjected Ran to a ceaseless barrage of attacks, always humiliating him in front of me and other people. It was heartbreaking,' he said.

'I'll never forget the first night. I went to sleep feeling awful for Ran and was very sad. The next morning I woke up and thought that today things will be better. Well, that day was just as bad.

'The only time we had any peace from her was when we went on runs, which perhaps explains why they always took so long [two to three hours].'

Mr Kobold claims that Sir Ranulph told him of an incident in which Mrs Millington-Cotes took his passport and locked him out of the house where they were living in Cheshire.

Sir Ranulph is said to have been injured as he attempted to climb back in through a bathroom window.

Mr Kobold claims that over several weeks, during which he was acting as Sir Ranulph's de facto chauffeur, he persuaded the explorer to divorce his wife.

'This was a firm decision and because Ran did not know how the mechanism works I was asked to basically organise everything around the divorce and manage it for him.'

Mr Kobold said he met a law firm in London and spoke over the phone to a PR specialist, because Sir Ranulph feared the divorce would 'get ugly' and he didn't want to 'be the next Paul McCartney' – a reference to the acrimonious split of Sir Paul McCartney and his second wife, Heather Mills.

But to Mr Kobold's surprise, Mrs Millington-Cotes arrived and insisted on talking to her husband alone.

'She shows up, kicks me out, slams the door shut and spends ten minutes with Ran,' Mr Kobold said.

'Afterwards he says, 'Mike, I've got bad news. Unfortunately I'm unable to move forward with the divorce.'

Days later, after Mr Kobold arranged a new passport, Sir Ranulph flew to Nepal for his second attempt at climbing Everest. Mr Kobold, who joined him at base camp, had previously seen a copy of the explorer's will and does not know why he wrote a new document on the eve of launching his climb.

'At base camp, for whatever reason, he created a new will. Something must have come into his mind. I just remember we were sitting in his tent and he wrote it out longhand and he signed it and he gave it to me.'

The legal status of the document is unclear because under English law, wills have to be signed by two witnesses. Mr Kobold said he may have signed the document, although he has no memory of doing so.

Sir Ranulph, then aged 65, was unable to reach the summit of Everest because of exhaustion, although he achieved the remarkable feat the following year, the oldest Briton to do so.

Mrs Millington-Cotes was approached for comment.