By Jon Cronin
BBC News business reporter
Copies of the new Potter book were sold ahead of its official release
It could have a been a plot worthy of Harry Potter's greatest adversary, the sinister Lord Voldemort.
Barely a week before the long-awaited publication of Harry Potter and the Half-Blood Prince, the latest adventure in the saga of the boy wizard, 14 copies of the children's book were inadvertently sold at a single store in Canada.
Revelations of the slip-up, and the ensuing court order to prevent any leak of the book's jealously-guarded storyline, made news headlines across the world.
But for one observer, the premature sales were a mistake waiting to be reported.
"I predicted that this would happen," says Stephen Brown, Professor of Marketing Research at the University of Ulster and author of Wizard! Harry Potter's Brand Magic.
"I said some books would go accidentally on sale. How could you accidentally sell the latest Harry Potter book?"
Harry Potter's success has made JK Rowling a very wealthy woman
Whatever the circumstances linked to sales, news of them has played a part in fuelling the hype surrounding the forthcoming worldwide launch of Harry Potter and the Half-Blood Prince.
On Thursday, a nine-year-old boy from New York state said he had returned a copy of the book mistakenly sold to him by a pharmacist - but only after glancing at the first few pages.
Few could doubt the literary and marketing success that is the Harry Potter series - from its relatively obscure origin with Harry Potter and the Philosopher's Stone in 1997 to the global publishing event that will be the sixth book's launch at 0001 BST on Saturday.
Accidental sales aside, publisher Bloomsbury has managed to keep the book's plot a secret - although betting shops reported a flurry of interest recently from punters predicting that Harry's mentor, Dumbledore, will die in the latest adventure.
For Professor Brown, the recipe for Harry Potter's success is a mixture of media hype, nostalgia - particularly among adult readers, and, of course, a growing series of books that have captured the imagination of children.
"Basically, its about storytelling," he says. "In order to make the sale you need to tell a tale people will buy into. There's the story of the author, the films, the merchandising. They all complement each other."
The global popularity of the books, films and games is estimated to have made the Harry Potter brand worth $1bn. More than 265 million copies of the books have been sold in 200 countries.
Author JK Rowling, whose rise to fame in itself is a marketing executive's dream, is reputedly now Britain's wealthiest woman.
Waterstone's booksellers estimates that on the first day of its release, the Half-Blood Prince will sell at least two million copies in the UK and more than 10 million worldwide.
Meanwhile, supermarket giant Tesco estimates that it will sell 300 copies a minute when the book finally goes on sale in the early hours of Saturday morning.
All this prompted US business magazine Forbes to comment recently: "If a visitor from another planet happened to browse a recent crop of US Securities and Exchange Commission filings, he might get the idea that Harry Potter runs a powerful Wall Street bank."
Naturally, the Potter phenomenon has been a boon for the book industry.
At a time when much of the retail market appears to be going backwards, shops have reported a 6% year-on-year increase in book sales.
Potter has been translated into 62 languages, including Chinese
"I wouldn't say Harry Potter has saved the UK book industry," says Neill Denny, editor-in-chief of the Bookseller magazine, "but clearly it's a positive development."
So, can anything dent the seemingly inexorable rise of the Harry Potter brand?
"If this book is no good then the seventh will flop, but I don't think that's going to happen," says Mr Denny.
Critics have complained that the previous two books - the Order of the Phoenix and the Goblet of Fire - were too long, but the titles nevertheless sold in their millions.
Perhaps only when the series finally draws to a close, with the seventh book, will the Harry Potter phenomenon come to rest.
However, with the film franchise some way behind the book - Harry Potter and the Goblet of Fire is due to hit cinema screens in November - it could be some time before Harry's fate is eventually known.
In the meantime, publishers are busy searching for what might replace JK Rowling's creation.
"There has been a massive search for the next Harry Potter by the children's publishers," says Mr Denny. "They haven't found him yet, mainly because Potter is still around."