She has sold more than 450 million books and amassed a personal fortune that saw her feature on Forbes magazine's billionaire list. But J. K. Rowling is well aware that the fickle finger of fate could still play another dramatic part in her rags-to-riches story.

The creator of Harry Potter says she remains stunned by the phenomenal success of the seven-book series featuring her teenage wizard.

''I can only tell the truth and the truth is that to the day I die I will not see myself the way many people see me now,'' she told Jennifer Byrne.

''Inside, I know I'm so grateful for what happened financially. But I'll never be used to it. I'll never take it for granted. And some part of me finds it quite hard to accept.''

Quoting from the great British comic writer, P. G. Wodehouse, Rowling said: ''Unseen in the background, Fate was quietly slipping lead into the boxing-glove.'' Whatever the weight of the boxing-gloves, nothing is likely to derail Joanne Rowling's imminent return to the top of the bestseller lists. Tomorrow - there's a worldwide embargo until 5pm - sees publication of her first adult novel, The Casual Vacancy, which has a reported first print-run of two million in both the US and Britain and many thousands in Australia. Pre-publication sales have seen the book in Amazon's top 10 for the past three months. The novel is set in the small English town of Pagford when a vacancy occurs on the local council. (One wag has already dubbed it Mugglemarch.) This is seen by some as an opportunity to offload an area of public housing that spawns significant social problems on to another council and leads to a clash between groups and people that reflect differing values and such issues as the English preoccupation with class, heroin addiction, poverty and adolescent sexuality.

Rowling reveals her disastrous and short-lived marriage to a Portuguese journalist that left her with a daughter to support was why she started writing the first of the Potter books, which she credits with dragging her out of depression.

Another marriage, six more Potter books, film adaptations and two more children have followed.

It was, she is quick to point out, no fairytale. ''Or if it was, it was one written by the Grimm brothers.''

Rowling is realistic about her new venture. She knows it will sell well, but not in comparison to the 12 million of Harry Potter and the Deathly Hallows, which until Fifty Shades of Grey was the fastest-selling book ever.

''Think how many books I could have sold if Harry had been more creative with his wand.''