US author Lionel Shriver has won the women-only Orange Prize for Fiction for her novel about motherhood gone wrong - We Need to Talk About Kevin.
Lionel Shriver said she thought she was going to win
Shriver's tale of a mother unable to love her son provoked fierce reactions for breaking a major parenting taboo.
The author picked up the £30,000 award in London on Tuesday and judges said Shriver's book was "very courageous".
The other nominated works were by Jane Gardam, Joolz Denby, Marina Lewycka, Maile Meloy and Sheri Holman.
In We Need to Talk About Kevin, the boy kills seven classmates at the age of 16.
The mother is left to examine their relationship to work out if she was to blame.
Shriver said she felt "a little unreal" and, after 20 years as a struggling author, was "not used to things going well".
But she said: "On some kind of sneaky, subterranean level, I thought I was going to win.
"I have been very ambitious from the start on this prize. I wanted it. I wanted it badly."
Chair of judges Jenni Murray, who hosts BBC Radio 4's Woman's Hour, said it would "resonate with everyone who has had a child or thought about having one".
Three shortlisted authors were from the UK, with three from the US
She said: "We Need to Talk About Kevin is a book that acknowledges what many women worry about but never express - the fear of becoming a mother and the terror of what kind of child one might bring into the world."
It is Shriver's seventh book and was originally published by the small US company Counterpoint Press after being rejected by a string of agents and major publishers.
But is soon became a word-of-mouth hit in New York in 2003.
Shriver, 48, changed her name to Lionel from Margaret Ann aged 15 because she thought men had an easier life.
She has lived in Nairobi, Bangkok and Belfast and now resides in London and New York with her husband, a jazz drummer.
The judging panel was chaired by broadcaster Jenni Murray (seated)
Jane Gardam had been the bookmakers' favourite for the Orange Prize for Old Filth, which records the reminiscences of an elderly QC who grew up in the last days of the Raj.
Also in the running was Marina Lewycka's debut, A Short History of Tractors in Ukrainian, which won an award for comic fiction at the Hay Festival on Monday.
The other British nominee was Joolz Denby, whose novel Billie Morgan is based on her life with a biker gang in Bradford.
Two other US writers were shortlisted - The Mammoth Cheese by Sheri Holman and Liars and Saints by Maile Meloy.
Best new writer
The six novels were selected from 120 books read by the all-female judging panel.
Last year's winner was Small Island by Andrea Levy, which went on to win Whitbread Book of the Year.
In addition to the £30,000 cheque, Shriver received a limited edition bronze figurine known as the Bessie.
Meanwhile, British author Diana Evans won the inaugural £10,000 Orange Award for New Writers with her debut novel 26a, about identical twins who retreat into their own world.