Poster for "This is Us"

Director Morgan Spurlock - who is helming the documentary 'This Is Us' about the British boy band - was keen to explore "why" certain people were so obsessed with the 'Little Things' hitmakers, and even interviewed medical experts for their opinions.

He told the New York Post newspaper: "We ask the question 'Why them?' We talked to this one doctor who tells us what happens inside a girl's body when she hears One Direction - like what happens in her brain and what goes on inside of her."

As well as exploring fans emotions, the 3D movie will also feature scenes of group hunk Harry Styles shirtless and Spurlock even filmed the five guys using the bathroom at the BRIT Awards earlier this year.

However, it is unlikely that Taylor Swift will appear in the film after Harry - who is joined in the band by Niall Horan, Zayn Malik, Liam Payne and Louis Tomlinson - reportedly ordered all footage featuring his ex-girlfriend to be removed.

A source said recently: "During their relationship producers shot Taylor and Harry in Los Angeles and New York City but Harry has ordered that none of it makes the cut. He wants nothing more to do with Taylor, she was a fling and they're done."