It's the saddest story Roald Dahl ever wrote - a poignant letter pleading for parents to vaccinate their children against measles, after his daughter died from the disease aged 7.
Dahl's 1988 plea for the Sandwell Health Authority in Britain urged everyone to vaccinate their children, and has resurfaced in the wake of the measles outbreak in California, where unvaccinated individuals have been infected by a contagious Disneyland visitor.
Olivia was Dahl's oldest daughter and in 1962 seemed to be recovering well from what was then a common childhood illness when she went rapidly downhill.
She had contracted measles encephalitis, which occurs in just 0.1 per cent of reported cases.
More than 20 years after Olivia 's death, Dahl, the author of such classics as Charlie and the Chocolate Factory, Boy, and Matilda, wrote to British parents.
"Olivia, my eldest daughter, caught measles when she was seven years old. As the illness took its usual course I can remember reading to her often in bed and not feeling particularly alarmed about it. Then one morning, when she was well on the road to recovery, I was sitting on her bed showing her how to fashion little animals out of coloured pipe-cleaners, and when it came to her turn to make one herself, I noticed that her fingers and her mind were not working together and she couldn't do anything.
"'Are you feeling all right?' I asked her.
"'I feel all sleepy,' she said.
"In an hour, she was unconscious. In twelve hours she was dead.
"The measles had turned into a terrible thing called measles encephalitis and there was nothing the doctors could do to save her. That was twenty-four years ago in 1962, but even now, if a child with measles happens to develop the same deadly reaction from measles as Olivia did, there would still be nothing the doctors could do to help her.
"On the other hand, there is today something that parents can do to make sure that this sort of tragedy does not happen to a child of theirs. They can insist that their child is immunised against measles. I was unable to do that for Olivia in 1962 because in those days a reliable measles vaccine had not been discovered. Today a good and safe vaccine is available to every family and all you have to do is to ask your doctor to administer it."
Dahl dedicated two of his books - James and the Giant Peach, and The BFG - to Olivia.
"I know how happy she would be if only she could know that her death had helped to save a good deal of illness and death among other children," he wrote.