By LEON WATSON
On thin ice: Sir David Attenborough with an anaesthetised polar bear in Svalbard during episode seven of the hit show Frozen Planet
The BBC's landmark wildlife documentary was four years in the making and took intrepid cameramen to the ends of the Earth to film.
But now it's been revealed the method used to capture key scenes might send a chill down the spine of Frozen Planet viewers.
Instead of being filmed in a sub-zero natural habitat, the BBC has admitted a polar bear and her cubs that were the centrepiece of the show were caught on camera in a zoo.
Moving scene: The pair of two-day-old polar bear cubs shown on the documentary. At this age they weighed less than a kilo, but were filmed in a zoo
The breathtaking footage was watched by more than eight million viewers. It showed a polar bear tending her newborn cubs but the snow was fake and real Arctic shots were mixed with zoo scenes.
The scene was filmed last Christmas in the comfort of a German wildlife park enclosure made of plaster and wood.
Faked? What the viewers saw on Frozen Planet turned out not to be filmed in the wild, but in a zoo in Germany
Situated beneath the zoo's polar bear enclosure, the den was fitted with cameras shortly before the cubs' birth.
Documentary makers have been accused of misleading the audience into believing the footage was gathered by daring cameramen in the wilderness.
The filming of the moving scene is explained by producer Kathryn Jeffs in a hard to find clip on the programme's website.
Mixed: The scene was mixed with real footage of polar bears in the wild, which may have misled viewers
She said it would be impractical to film the carnivores in the wild, adding: 'They stay in the pole through the winter and the female polar bears actually give birth at the peak of winter.
'The problem for us is that they do it underneath the snow in these dens of ice and there's absolutely no way we can get our cameras down there.'
But during the show Sir David Attenborough's script failed to explain how the key scene was made.
The documentary drew in eight million viewers transfixed by moving scenes of a polar cub being born