Grace McCleen has won this year's Desmond Elliott Prize with her novel, The Land Of Decoration, but says her writing career has come to an end.
The Welsh author took the £10,000 at a ceremony on Thursday evening at Fortnum & Mason in London.
Grace McCleen was successful over a longlist of 10 other novels nominated for the new fiction prize, including Patrick McGuinness's The Last Hundred Days and Absolution by Patrick Flanery.
Accepting the award from the judges, a shocked Grace McCleen said "I was so sure I wasn't going to win that I haven't prepared anything to say."
She joked: "I am a bit disappointed I haven't got the hamper, but I suppose I'll buy one now!
McCleen thanked her editor, agent and publicity people who she said were her friends as well as her colleagues.
The judging panel chair Sam Llewellyn said her novel "transported the reader to a completely plausible but really peculiar world" and was a "worthy winner".
He continued, "Grace McCleen's voice sparkles with imagery and ideas, and she uses it to tell a story that is simultaneously multi-layered and absolutely compelling."
The Land Of Decoration, which was published in March 2012, was described by the judges as "unlike anything you have ever read". The novel was praised for its inventive narrator, 10-year-old Judith McPherson who believes she can work her own miracles as an escape from school bullies.
Like her protagonist, McCleen was raised in a Welsh fundamentalist Christian sect, and was removed from school at the age of 10. As well as winning the Desmond Elliott Prize, McClean has been selected as one of Waterstone's most promising young novelists this year. The Land Of Decoration was named as a must-read novel by The Sunday Times.
McCleen announced on her website that she had just finished writing her fifth novel, which will be "the last I will write". She wrote, "I would like to concentrate on music from now on, which I would love to have pursued when I was younger."
The author has also written four books prior to The Land Of Decoration, which will now be published as a result of the novel's success.