Natasha Richardson cried during Everest film role. Weeks later, she too died on a mountain

In the last film she made, Natasha Richardson sobbed as she recorded the words of a woman learning her husband would never return from Everest.

Two months later, the 45-year-old actress died in her own mountain tragedy, leaving the documentary drama, The Wildest Dream, as her final work for the big screen.

The film, telling the story of British explorer George Mallory's final attempt on Everest in 1924 and how his frozen body was discovered eight decades later, has now been dedicated to the actress. Richardson, elder daughter of Vanessa Redgrave, voiced the part of Mallory's wife, Ruth.

The Wildest Dream will receive a special charity screening at the BFI Imax in London, attended by Richardson's family, for HIV charity The National Aids Trust before its release next month.

Irish actor Liam Neeson, her husband and the project narrator, described it today as "not just a film about mountain climbing" but "a passionate love story between George and Ruth Mallory and an extraordinary tale of one man's curiosity, courage and conviction".

He added: "[Natasha] was as gripped with the Mallorys' story as I was. As we all know, this was her final performance and I know she was very proud to be part of this compelling story."

Director Anthony Geffen described the poignant final day of recording when the actress wept as she read the telegram telling Ruth her husband had died. It remains a hotly disputed issue whether the man who famously wanted to climb Everest "because it is there" became the first to make the summit.

When mountaineer Conrad Anker found the body in 1999, the photograph of Ruth that Mallory had promised to leave at the top of the world could not be found. Anker recreates the discovery in the film. Geffen, 47, said Richardson had to stop for coffee and to compose herself before completing the recording.

"She started to cry and she turned and said to me, 'Gosh, I'm finding this hard to read because I can't quite imagine what it would be like if this letter was about Liam, or if this was Liam and he was reading about me not coming back'." Two months later, in March last year, she was dead after a skiing accident in Canada. Geffen showed the finished film to Neeson this year. "It was very hard for him to sit there and listen to Natasha's voice, but he loved the film," he said.

The charity event is on September 21 and the film opens three days later.