Thousands of Harry Potter fans braved rain and hail yesterday to cheer the cast of "Harry Potter and the Half-Blood Prince" at its London premiere.

Stars Daniel Radcliffe, Emma Watson, Rupert Grint and other cast members, along with the boy wizard's creator, J.K. Rowling, walked up a soggy red carpet before the screening in Leicester Square.

The sixth Potter film, "Half-Blood Prince" sees Harry and his friends at Hogwarts school battling evil Lord Voldemort — and their raging teenage hormones.

The cast members wore white ribbons in memory of Rob Knox, a young actor in the film who was stabbed to death in London last year.

The movie opens around the world July 15.

PUZZLES LEAD UP TO BROWN'S NEW RELEASE

The promotion for Dan Brown's new thriller will itself be a bit of a puzzle.

Publisher Doubleday announced yesterday that Brown's "The Lost Symbol" — his first novel since "The Da Vinci Code" — will be preceded by a summerlong procession of "codes, cryptic trivia, puzzles, secret history, maps, aphorisms" and other daily teasers on Facebook and Twitter.

The book, which comes out in the fall, will be set in Washington, D.C., and will feature "Da Vinci Code" protagonist Robert Langdon, again caught up in secret societies and hidden codes.

"The Lost Symbol" has an announced first printing of 5 million.

HANKS BACK ON ACADEMY AWARDS BOARD

Tom Hanks is rejoining the board that oversees the Academy Awards.

After a one-year hiatus, Hanks was elected yesterday to a new three-year term on the board of governors representing the actors branch of the Academy of Motion Picture Arts and Sciences.

Hanks was among nine incumbents and four new members elected to the board.

But a rare runoff vote is needed after two directors tied for a seat on the board.

Filmmaker Edward Zwick, who directed "Blood Diamond" and "Glory," and frequent Oscar ceremony producer and director Gil Cates tied for a seat representing the directors branch.

HOLLY MADISON GUESTS AS OCTAGON GIRL

Already in Las Vegas for her Planet Hollywood production "Peep Show," Holly Madison will make the rounds Saturday night as an Octagon Girl at UFC 100.

The fight card at Mandalay Bay is expected to be the biggest event in Ultimate Fighting Championship's history with a unified heavyweight title match between Brock Lesnar and Frank Mir and a welterweight championship fight between Georges St-Pierre, who recently defeated Hilo's B.J. Penn, and No. 1 contender Thiago Alves.

And the Octagon Girls — Arianny Celeste, Edith Labelle and Logan Stanton — will be joined by former "Girl Next Door" star Madison, who also appeared on "Dancing With the Stars."