The clip opens with Harry, in his Defence Against the Dark Arts class, surprised to find Professor Snape telling the class to "turn to page 394".
But then it moves to great shots of the huge Knight Bus screaming through dark wet streets, throwing Harry around the bus as it does.
In one of the bus scenes, there is an odd-looking beast with dreadlocked hair who appears to have been created for the film.
We hear the news that Sirius Black, played by Gary Oldman, has escaped from Azkaban prison and Harry is warned not to go looking for him.
There is also a nice shot of Ron and Hermione holding hands!
The trailer ends with Hermione calling Draco Malfoy an "evil little cockroach", before punching him saying "That felt good".
The world premiere of the latest Potter movie is expected to be held in the US on 23 May, probably in New York, with the first UK showing seven days later.
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