Natasha will be reunited in film with her husband Liam Neeson in a documentary about the British explorer George Mallory this summer.

The Wildest Dream is a love story which charts how Mallory was torn between his love for his wife Ruth, and his obsession with the “last great adventure”, becoming the first person to climb the highest mountain, Mount Everest.

Ruth Mallory is voiced by Natasha Richardson in her final role before she was killed in a skiing accident in Canada last year. The film is dedicated to Richardson, whose readings of Ruth Mallory’s love letters to her husband have been described as “especially heartfelt and moving”.Liam Neeson, who was married to Richardson for 15 years until her death, narrates the film which is being released in August.

Mallory, who was dressed in gabardine and wearing hobnailed boots, was last seen alive 800ft below the summit before he disappeared in 1924.

The documentary tells the intersecting stories of Mallory and Conrad Anker, the mountaineer who discovered Mallory’s frozen remains in 1999.

All of Mallory’s belongings were found intact on his body, except a photograph of Ruth, which he had promised to leave at the “top of the world” if he succeeded.

In 2007 Anker returned to Everest to try and get a better understanding of what happened to the explorer. Using replica 1920s-era clothing and equipment and retracing the original route, Anker set out to solve the mystery of whether Mallory succeeded in reaching the summit.

The film tells the story through the modern day expedition, the explorer’s letters to Ruth and previously unseen photos and film archive from 1924 which has been restored.

The actor Ralph Fiennes provides the voice of Mallory, Hugh Dancy voices Mallory’s fellow climber Andrew Irvine and Alan Rickman is Noel Odell, the last person to see Mallory alive.

The director Anthony Geffen said: “Mallory fascinates me because he dared to dream the impossible. In a golden age of exploration, he was the pioneering adventurer determined to reach into the world’s last great, untouched wilderness. The Mallory story is still as tantalizing and compelling today as it was in 1924.”

Mallory is famously quoted as having replied to the question “Why do you want to climb Mount Everest?” with the retort: “Because it’s there”, which have since been described as the most famous three words in mountaineering.

The Wildest Dream, released under the National Geographic World Films, has already been screened at the 2009 Toronto Film Festival.

Lisa Truitt, president, National Geographic Cinema Ventures, said: “The film is dedicated to Richardson, whose readings of Ruth Mallory’s love letters to her husband are especially heartfelt and moving.”

Source