PLANET Earth II producers were devastated during filming when they saw 150,000 antelope killed off in just three days.
The Saiga Antelope of Kazakhstan is the focus of part of the forthcoming episode airing on Sunday night.
However, producer of the Grasslands instalment, Chadden Hunter, revealed a shocking disease went round while they were filming and they witnessed thousands of them dying in the short space of time.
He said: “When we were out there in the calving grounds, with hundreds of thousands of females all giving birth at the same time, a very virulent disease swept through the population and killed around 150,000 of them in a matter of three days.
“At the time we thought we were watching the greatest natural catastrophe that I’d ever heard of.
“We watched 150,000 of these magnificent animals die in front of us.
“At the time we didn’t know if this was the final extinction of the species, which was devastating, emotionally, for the crew.”
However, they did later discover that many of the babies had managed to survive.
He said: “We since heard that the last few mothers and babies we filmed have survived.
“It was a potent reminder of how fragile yet resilient nature can be.”
Chadden also admitted going so far and seeing nature in the way was an amazing experience.
He said: “To go somewhere so remote to see an animal that looks like it’s from another planet was just incredible.”
The David Attenborough-narrated series continues to be a huge ratings success, gaining nearly 10 million viewers an episode.
In recent episodes, viewers were left shocked when a pride of lions attacked a giraffe – and lost – and a bat fought with a scorpion and won.
However, some have been upset to learn that Planet Earth scenes have been faked.
Back in April, bosses admitted that the sound needed to be edited to that background noise was eliminated.