Sir Edmund Hillary outlined his final wishes to family back in New Zealand just days before attempting to become the first person up the world's tallest mountain, a remarkable forgotten letter has revealed.

Sixty-six years after Hillary, along with Nepalese Sherpa mountaineer Tenzing Norgay, conquered Mt Everest, a letter home from a high-altitude base camp has surfaced publicly for the first time.

As preparations for the daring expedition's final push ramped up in the shadow of the daunting 8848m rock behemoth, the pragmatic Auckland beekeeper seems to have accepted he could die trying.

"We have a tremendous task in front of us," he writes to brother Rex Hillary on May 20, 1953 from Camp IV Advanced Base – nine days before reaching the summit and becoming one of the world's most famous men.

"Our oxygen gear is still pretty experimental, so remember in the unfortunate business of anything going wrong that my two main wishes are that Mother should be looked after and secondly that my Himalayan gear should go to the NZAC [New Zealand Alpine Club] for their use.

A forgotten letter by Sir Edmund Hillary just days before his world-first ascent of Mt Everest has surfaced for the first time. Photo / Supplied

"Sounds morbid, I know but I expect I'll still be demareeing [beehive swarm prevention method] next November despite it all."

The handwritten document, in which an otherwise confident Hillary expressed an admiration for his fellow climbers, is now being sold by nephew John Hillary.

It is expected to generate national and worldwide interest when it goes up for auction this month.

Auctioneer Andrew Grigg of Cordy's Auctioneers in Remuera said it's "part of our taonga" and urged museums to consider picking it up at the February 26 sale.

A forgotten letter by Sir Edmund Hillary. Photo / Supplied

"I believe it's certainly of institutional interest," he said.

"It gives amazing insight into one of our most famous New Zealanders."

New Zealand's national museum Te Papa in Wellington said it "doesn't comment on auctions".

The Ministry for Culture and Heritage monitors domestic auctions and has strict rules about historical New Zealand objects leaving the country.

John Hillary has agonised over the decision to sell the letter, along with other letters and postcards, and a rock fragment his famous uncle collected from Everest's summit as a memento and later got made into a Nepalese pendant.

"It's not something I really wanted to do," said the 70-year-old.

"My preference would be that they would be available to the public … but I can't determine that, because I've put them in the auction, and that's it. Whether it's the right or wrong thing to do … it's a done thing now.

A rock fragment collected by Sir Edmund Hillary. Photo / Supplied

"If I would have one piece of advice for young people in this country, it would be to get something going as soon as you can for your retirement, because the pension just doesn't cut the mustard."

Lady June Hillary – Sir Ed's second wife – donated rock shards collected as a memento atop Everest, along with other artefacts, to Otago Museum in 2010.

A bitter family feud erupted around the same time when Lady June tried to sell some of Sir Edmund's watches – including one he wore on a South Pole expedition – at auction in Switzerland.

Sir Edmund's children, Peter and Sarah Hillary claimed the watches belonged to them and should not have left the country. They successfully blocked the sale through a High Court injunction.

Peter Hillary was in Japan yesterday. His wife Yvonne Oomen said Peter was aware of the auction and that he was supportive of John.

"It's unfortunate he has to [sell the items] but we understand these things," she said.

New Zealand-born mountaineer Sir Edmund Hillary sits at base camp, preparing for his successful attempt to be the first to reach the summit of Mount Everest, Nepal, May 1953. Photo / Supplied

John was almost 5 years old when his beloved Uncle Ed scaled Everest. He followed his progress on the wireless and in newspapers, cutting clippings for a scrapbook that is still in his possession.

John recalls a fun-loving and amiable uncle who always had time for his nephew.

"He was a great uncle. I loved him very much," he said.

"For me, the things that are absolutely important, and which I hold very dear and close to my heart, are not the physical things, but our relationship."