The teenage author of a website dedicated to Harry Potter was recently woken up by a magical phone call: J.K Rowling inviting him to interview her as she launches the sixth book in the Harry Potter series.

Emerson Spartz, 18, from Indiana in America, was asleep at nine o'clock in the morning when the telephone rang. According to the account on his website, Mugglenet, Ms Rowling started the conversation: "Hello, Emerson? This is Jo... You believe me, don't you?"

Mr Spartz was invited by the secretive Ms Rowling, her publishers have confirmed, because of the high quality and popularity of his website.

Along with Melissa Anelli, a reporter at The Staten Island Advance, a local New York City newspaper, and the author of another popular Harry Potter website, The Leaky Cauldron, he will get the chance to interview Ms Rowling for an hour on the day of the launch of Harry Potter and the Half Blood Prince on July 16.

Both Mr Spartz and Ms Anelli were told to keep their invitations secret until Bloomsbury, the publishers of the Harry Potter series, had made an official announcement.

Mr Spartz and Ms Anelli will take part in a weekend of interviews with Ms Rowling at Edinburgh Castle. Seventy other young journalists will also be invited to read the book on the weekend it is published and put their questions to Ms Rowling.

Bookshops and newspapers across the world, including The Times, are running competitions to select the lucky few who will take part.

Mr Spartz and Ms Anelli received calls from Ms Rowling on the same day in early May, but Ms Anelli had been warned to expect some kind of invitation. Mr Spartz was taken completely by surprise, although in an email conversation with Ms Anelli posted on her website, Mr Spartz said that he managed to control himself when he realised who he was talking to.

"I keep my emotions in my head," wrote Mr Spartz. The rest of the email conversation was then dominated by many exclamations of "Oh my God".