The author of Watership Down, Richard Adams, has died aged 96, his daughter has said.
Juliet Johnson said her father had been "ailing for some time" but "died peacefully" on Christmas Eve.
Watership Down, a children's classic about a group of rabbits in search of a new home after their warren was destroyed, was first published in 1972.
Adams was 52 when he wrote it, after first telling the story to his two daughters on a long car journey.
It went on to become a best-seller, with tens of millions of copies bought around the world.
Watership Down was made into a film version in 1978 and enjoyed huge success, but was notoriously frightening for young children, with its graphic, apocalyptic scenes of impending doom.
The film's theme song Bright Eyes, sung by Art Garfunkel, spent six weeks at the top of the UK charts the following year.
Mrs Johnson told BBC Radio 4 she had a "long talk" with her father on the night before he died.
"I assured him that he was much loved, that he had done great work, that many people loved his books," she said.
She said an upcoming adaptation, which is due to air on the BBC next year, gave Adams "great composure and comfort".
Describing Christmas Eve a "rather a magical night", she said: "It's the night that traditionally the animals and birds can talk.
"It was absolutely typical of Dad that he would choose such a night on which to leave this world."
Adams, a former civil servant from Newbury in Berkshire, also wrote Shardik, The Plague Dogs and The Girl in a Swing.
Watership Down won the Carnegie Medal for children's fiction in 1972, the year of publication, despite having been rejected by several publishers.
A statement on a website devoted to the book said: "Richard's much-loved family announce with sadness that their dear father, grandfather, and great-grandfather passed away peacefully at 10pm on Christmas Eve."
The statement marked his death with a passage from his best-known work.
"It seemed to Hazel that he would not be needing his body any more, so he left it lying on the edge of the ditch, but stopped for a moment to watch his rabbits and to try to get used to the extraordinary feeling that strength and speed were flowing inexhaustibly out of him into their sleek young bodies and healthy senses.
"You needn't worry about them," said his companion. "They'll be alright - and thousands like them."
Adams, a World War Two veteran, was head of animal welfare charity the RSPCA for a short spell.
Obituary: The man who turned a car story into a best-seller
By Nick Serpell, BBC obituary editor
The event that changed Richard Adams' life occurred on a car journey with his family to see Twelfth Night at Stratford-upon-Avon.
His bored children asked for a story and he began telling them a tale about a group of rabbits attempting to escape from their threatened warren.
Adams was persuaded to write it all down, a process that took him more than two years, but he was, at first, unable to find a publisher.
Many of his rejection letters complained that the book was too long and his characters did not fit the common perception of cuddly bunnies.
Eventually, in 1972, after 14 rejections, the publisher Rex Collings saw the potential and agreed to take it on with an initial print run of 2,500 copies.
A spokesman for Oneworld publications, which brought out a new edition of Watership Down with illustrations by Aldo Galli in 2014, said they were "very saddened" at his death.
"His books will be cherished for years to come," the spokesman said.
A new animated series of the book, co-produced by the BBC and Netflix, is due to be aired in 2017 with four hour-long episodes.
Sir Ben Kingsley, Olivia Colman and John Boyega have been cast to provide voices in the new adaptation.