Harry Styles' parents miss their son.

Dad Des Styles and mum Anne Cox - who married her long-term partner Robin Twist in June, with Harry acting as best man - revealed their feelings in intimate interviews which feature in the band's 3D documentary film "One Direction: This is Us" - which had its world premiere on Tuesday (20.08.13).

Des said: "Harry went as a kid to 'The X Factor' and never came home."

Anne also admitted she worries her 19-year-old son's success could be short-lived.

She said: "[The fame could] come crashing down. There is always this feeling you have to be ready to pick up the pieces and we've been waiting to - but it just gets bigger and bigger."

Liam Payne's father also became emotional during a scene in the film when he explained how much he has missed his son since he entered Simon Cowell's talent show aged just 16.

Geoff Payne said: "He's the only lad in the family and now that's gone I'll never get it back.

The group were all in attendance for the 'One Direction: This is Us' premiere in London's Leicester Square on Tuesday night where they were greeted by thousands of screaming fans - some of which had camped outside two days prior get a prime spot to see their idols.

Liam - who is also joined in the band by Zayn Malik, Louis Tomlinson and Niall Horan - admitted it was difficult for him to watch his father's confessional in the documentary.

The 19-year-old star said:"He's always so happy when I see him. To actually see what he's like when I'm not there was a bit mad."

After signing autographs and taking photos with fans, the boys moved onto private members' club Soho House when the premiere ended to celebrate.