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Director Peter Jackson premiered his First World War documentary They Shall Not Grow Old on Tuesday, urging those whose family fought in the conflict to talk to their elderly relatives with knowledge of it before it is too late.

The Oscar-winner, known for The Lord of the Rings and The Hobbit movies, presented his edit of footage from the Great War at the BFI London Film Festival, where he was joined by Britain’s Prince William on the red carpet.

The film takes the viewer to the front lines, with archive video footage from the trenches brought to 3D life by colourists and actors voicing conversations between soldiers there, which were deciphered by forensic lip-readers.

“There’s nobody alive that fought in the First World War but some people have probably got grandparents that their parents were in the First World War so now is the last time that people can ask questions in their family,” Jackson told Reuters.

“If you have any grandparents that their parents were in the First World War start to ask them questions because at some point in the future that opportunity won’t be there. It’ll be very hard to find out anything.” An estimated 17 million people were killed in the war, many of them on the battlegrounds in northern France and Belgium.

Around 1 million of those who died were from Britain and its then-empire.

Voiced by former soldiers, They Shall Not Grow Old shows how the men, some of them young teenagers, trained for fighting and survived or perished in the fighting.

“What stood out for me once we saw the footage was that the men in the pictures were exactly like us,” Jackson, whose grandfather fought in the conflict, said.

Supporting the director at the film’s world premiere was actor Dominic Monaghan, who starred in The Lord of the Rings and visited Jackson in his native New Zealand when he was working on They Shall Not Grow Old.

“I think Pete was struck more than anything else by the youth of the people that were in the war,” Monaghan said.

The Lost actor is set to make an appearance in Star Wars Episode IX, the last film in the latest trilogy of the sci-fi saga. Asked if he could reveal anything about the movie due for release next year, he said: “Nothing, I’ll get in trouble.”