The writer’s widow, Fanny, wrote to a close friend the day after the Edinburgh-born author collapsed and died from a suspected from haemorrhage at their home in Samoa in 1894.
It was one of a series of letters sent by the couple to Anne Jenkin, the wife of the author’s former Edinburgh University tutor and professor of engineering, Fleeming Jenkin.
They have been secured by the National Library of Scotland after Stevenson experts spotted them being sold off by Christie’s in London.
They were put up for sale by Mrs Jenkin’s descendants, along with essays, telegrams, photographs and newspaper cuttings.
In the letter written by Fanny Stevenson about the writer’s death, she says: ““His life had been one long romance and he hoped to have a romantic end; the artist in him demanded that completeness.
“To grow old he could not bear. He has had his wish and, for that, I try to be thankful, though all the rest of my life will be empty and lonely. True, I have my children but I have not Louis. No one knows what that means but me.”
Mrs Stevenson reveals that her husband her collapsed when they began to make to make mayonnaise for dinner.
She added: “I began to mix the mayonnaise; he dropping the oil with a steady hand, drop by drop. Suddenly, he set down the bottle, knelt by the table, leaning his head against it. I cannot go on just now.
“It was the hand of death that had stricken him down. In less than five minutes he was profoundly insensible and so remained till the end. It was about six when he knelt at the table and at ten minutes after eight, he passed away. In a very short time, we had two doctors and a medical missionary here but there was nothing to do.
“That very day he had said to me ‘the thought of dying in bed is horrible to me; I want to die like a clean human being on my feet. I want to die in my clothes, to fall just as I stand.’ He did. It was only at the very end, for the last few breaths, that we laid him down.”
The Jenkin papers are the biggest acquisition by the library of Stevenson-related material since it acquired a collection built up over half a century by Dr Ernest Mayhew, the world’s leading Stevenson scholar, after his death in 2011.
Scotland’s national librarian, Dr John Scally, said: “It is pleasing that these letters relating to one of Scotland’s greatest ever writers are part of the collection in the city and the country of his birth. They are sure to be of interest to scholars and the wider public and we are delighted to have acquired them.”