NEW YORK (CNN/Money) - The sixth book in the popular Harry Potter series will be titled "Harry Potter and the Half Blood Prince," the books' author J.K. Rowling has announced.

The title of the sixth Harry Potter book will be "Harry Potter and the Half Blood Prince."

Rowling made the announcement on her Web site, JKRowling.com, although it took some knowledge of her site by dedicated fans to reveal the title. The path to find the title was explained on a fan's site, WizardNews.com, and was confirmed Tuesday by her literary agent, Christopher Little Agency, which was reached in London by CNN/Money.

Rowling is still in the process of writing the book and no release date has been set, according to her agent. The fifth book in the series, "Harry Potter and the Order of the Phoenix," was published in 2003, and is due out in paperback version in Britain on July 10 and in the United States on Aug. 10.

Overall the first five books in the series have sold more than 250 million copies worldwide since the debut of the first book, "Harry Potter and the Sorcerer's Stone," in 1997. The British publisher of the books is Bloomsbury Publishing PLC, while the U.S. publisher is Scholastic Corp. (SCHL: Research, Estimates)

The first three books have been turned into movies. The third, "Harry Potter and the Prisoner of Azkaban," is still in theaters. Between them the first three films have have done box office of $2.4 billion worldwide, through June 27, after costing just less than $500 million to film and market, according to Hollywood tracking firm Box Office Mojo.

The fourth movie, "Harry Potter and the Goblet of Fire," is due in theaters in November 2005. The first four movies are all from Warner Bros., which like CNN/Money is a unit of Time Warner (TWX: Research, Estimates).

A "rumors" section of the site had included a post from fans Monday that the new title would be "Harry Potter and the Pillar of Storge" but Rowling dismissed that idea on the site, saying, "I am trying very hard not to be offended that anyone thought this was possible."

Another posting in the rumor section said that the title would be "Harry Potter and the Toenail of Icklibogg" to which Rowling responded, "Well, if you believed the Storge one..."

On her site's main "Daily News" page Rowling wrote, "Well the door opened at last and I showed you the title of book six -- the genuine title, the title that will appear on the published book, the title I have been using in my head for ages and ages. Unfortunately, however, the door opened on the very same day the 'Pillar of Storge' hoaxer struck."

Rowling said that she had once considered the new title for her second book, "Harry Potter and the Chamber of Secrets."

"Certain crucial pieces of information in book six were originally planned for 'Chamber of Secrets,' but very early on I realized that this information's proper home was book six," she wrote on the home page.

She seemed to confirm the Half Blood Prince title on the Daily News page by adding "The HBP is neither Harry nor Voldemort," she wrote. Lord Voldemort is the series' villain.