Katy Perry's fans who attended a preview screening of her film Katy Perry: Part of Me were given a special surprise in London when the star of the film turned up in person at the venue to introduce the film herself.

Completely unaware of Katy’s appearance in advance, the awe-struck crowd cheered and applauded as she made her way into the auditorium, where she also took time to hand out 3D glasses and popcorn to her audience.

She told the crowd, "Hey, hello! Is it alright that I'm here? We're going to watch my movie!" before she put on her own glasses, and sat down in the middle of the cinema to watch the film herself.

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Perry has been making the most of her time in London, sparking rumours of a rekindled romance with her ex Robert Ackroyd, and downing pints in a Hackney pub.

Her film is in UK cinemas on 5 July, and the singer has already promised it will be a warts-and-all look behind the apparent glamour of her superstar life.

And she also found time to record a slot on Graham Norton's show, where she got pally with Cheryl Cole. Pictures here...

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