"Fifty Shades of Grey" has become the bestselling British book of all time.
The first book in E.L. James' erotic novel trilogy has sold more than 5.3 million copies, according to figures released today by its publisher, Random House.
The second and third installments of the phenomenon - "Fifty Shades Darker" and "Fifty Shades Freed" - have sold around 3.6 million and 3.2 million copies respectively.
Ms James said the news was "totally unexpected" as she had "no idea they would be so successful".
The book has become a global success and the trilogy is being published in a variety of languages, including Albanian, Chinese, Russian, Serbian and Vietnamese.
"Fifty Shades" is also set to hit the big screen as part of a movie franchise.