WATFORD, England -- It's official: Eight will be the magic number for the " Harry Potter" film franchise.

After months of rumors, Warner Bros. and the producers of the massively successful movies will announce Thursday that they plan to split "Harry Potter and the Deathly Hallows," J.K. Rowling's seventh and final "Potter" novel, into two blockbuster films -- one to be released in November 2010 and the second in May 2011.

The films will be titled, simply, "Harry Potter and the Deathly Hallows: Part I" and "Harry Potter and the Deathly Hallows: Part II," according to producer David Heyman. Director David Yates, who returned for his second tour of Potter duty with "Harry Potter and the Half-Blood Prince" and is quite popular with the cast, will direct both "Deathly Hallows" films, which will be filmed concurrently. Screenwriter Steve Kloves also returns and, by completion of the franchise, will have written seven of the eight films.

One devoted "Potter" reader that is especially happy to hear the news is Daniel Radcliffe, the 18-year-old actor who plays the title character in the wizardry epic.

Some cynics will see the move as simply doubling the box-office payday, but Radcliffe told The Times that the split is purely in service of the story.

"I think it's the only way you can do it without cutting out a huge portion of the book," Radcliffe said recently during a break on the set of "Half-Blood Prince," the sixth "Potter" film, which is due in theaters on Nov. 21. "There have been compartmentalized subplots in the other books that have made them easier to cut -- although those cuts were still to the horror of some fans -- but the seventh book doesn't really have any subplots. It's one driving, pounding story from the word go."

Producer David Heyman said the decision was made with some anxiety and only after considerable deliberations. The producer joked that "while my wife and Warner Brothers were pleased" to hear that the Potter movie magic will continue into the next decade, he himself fretted that the cynical observers would see the decision as a purely mercenary move.

"I swear to you it was born out of purely creative reasons," Heyman said during an interview in a converted airplane factory outside London that has been home base to all of the "Potter" productions. "Unlike every other book, you cannot remove elements of this book. You can remove scenes of Ron playing quidditch from the fifth book, and you can remove Hermione and S.P.E.W. [Society for the Promotion of Elfish Welfare] and those subplots . . . but with the seventh, that can't be done."

Heyman said he approached Rowling with some trepidation about the strategy but found that she signed off on its logic rather quickly. "I went to Jo and she was cool with it," Heyman said, "and that was quite a relief."

Rowling has also been a more frequent visitor to the sixth movie's set than with previous installments. One big reason is that she is no longer busy trying to finish the "next" Potter book; she walked away from her signature character in July 2007, when the climactic "Deathly Hallows" hit stores, and continued the history-making ways of the series by selling 11 million copies during its first 24 hours on shelves.

The filming of "Half-Blood Prince" began in September, and Radcliffe said "it's been brilliant." He added: "It's also, I think, the funniest of the films so far."

The "Potter" films have pulled in a staggering $4.5 billion at the box office worldwide. Heyman said now that the "Potter" team knows they can split "Deathly Hollows" in half, the next challenge is figuring out the division.

As Heyman put it: "The question will be, where do you break it? And how do you make them one but two separate and distinct stories? Do you break it with a moment of suspense or one of resolution? These are the interesting challenges. But each book has presented its challenges."

Warner Bros. Chairman Alan Horn and Jeff Robinov, president of Warner Bros. Pictures Group, are expected to discuss the new plans for "Potter" on Thursday during a presentation at ShoWest, the convention of movie exhibitors in Las Vegas.

geoff.boucher@latimes.com