Researchers have identified a language new to science in a remote region of India.
Known as Koro, it appears to be distinct from other languages in the family to which it belongs; but it is also under threat.
Koro was discovered by a team of linguists on an expedition to Arunachal Pradesh, in north-eastern India.
The team was part of National Geographic's "Enduring Voices" project on threatened indigenous languages.
The researchers were searching for two other little-known languages spoken only in one small area.
As they heard and recorded these, they found a third which was completely new to them and had never before been listed.
"We didn't have to get far on our word list to realise it was extremely different in every possible way," said Dr David Harrison, one of the expedition leaders.
The linguists recorded thousands of words- and found Koro was distinct from other languages in the area.
It belongs to the Tibeto-Burman family, which includes around 150 languages spoken in India. But scientists were unable to find any others closely related to Koro within this group.
It is thought that around half of the world's 6,909 known languages are endangered and Koro itself is vulnerable. It has never been written down and is only spoken by between 800 and 1,200 people.
"We were finding something that was making its exit, was on its way out," said National Geographic Fellow Gregory Anderson.
"And if we had waited 10 years to make the trip, we might not have come across close to the number of speakers we found."
The team will be returning to India next month to continue their research on Koro.
They want to find out more about where it came from and how it was able to remain hidden until now.