The final installment of the Harry Potter films will be the darkest yet, based on the trailer released in Britain Wednesday by its distributor, Warner Bros.

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The "Harry Potter and the Order of the Phoenix" trailer opens with Hogwarts' Keeper of the Keys and Grounds Hagrid warning Harry:

"It's changing out there Harry," he says. "A storm is coming Harry, just like last time."

In the film, based on J.K. Rowling's best-seller, wizard-in-training Harry must battle both Voldemort and an increasingly authoritarian Hogwarts school, the London Telegraph said Wednesday.

The movie will be released in July, the same month as the final Harry Potter book, "Harry Potter and the Deathly Hallows."