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The film examines the difficult period in Beckham's life after he was sent off at the 1998 World Cup.
"There will be a few tears in there from my mum I'm sure," Beckham said.
The former England captain said he valued the support of his teammates throughout tough moments of his career.
"It's the same for all of us six. There were good times, there were bad times, there were troubled times where we all stuck together," he said.
"But that is part of the movie, part of the history of the six of us.
"That is why it makes this such a great story."
Class of '92 stars David Beckham, Paul Scholes, Nicky Butt, Ryan Giggs and Phil and Gary Neville arrived at the documentary's premiere at Leicester Square.
The former England captain attended the event with wife Victoria, and the couple's three sons Brooklyn, Romeo and Cruz.
When asked about reports that Beckham could become Sir David in the New Year Honours List, Styles replied: "Why not? He's a national treasure isn't he? It makes sense. I thought he was already."