A fable about friendship and loss has beaten bestselling novels The Girl on the Train and Go Set a Watchman to be named Waterstones Book of the Year.

The Fox and the Star, by first-time author Coralie Bickford-Smith, is about a fox in a forest who loses his only friend, a star in the sky.Bickford-Smith, who works as a senior book designer for Penguin, said she was "touched and honoured" to win."It's totally unexpected, it doesn't feel real," she said.

The designer-turned-author took a six-month sabbatical from work to write and illustrate the book. "I wanted it to be a children's book but it's for adults as well," she told the BBC, citing inspiration William Blake's short poem Eternity and the graphic work of William Morris.

"It's about love, loss and learning to accept change. Everyone's been though loss. I lost my mum while I was at university, it resonated with that. "But art has to be magical and mysterious, and I want people to project their own emotions onto it."

Bickford-Smith, whose design work includes cloth-bound editions of Penguin Classics, said her debut was "a blend of classical old book design with a modern twist". "It celebrates the book as a physical object," she added.