The bird, Sillem's Mountain Finch, has been a mystery since the first specimens were collected in 1929 and were identified as a distinct species in 1992 from specimens collected in Tibet's Karakoram Mountains.
The area -- a disputed border region of China, India and Pakistan -- is inaccessible to zoologists.
When Dutch ornithologist Kees Roselaar examined the two 63-year-old specimens in the Amsterdam Zoological Museum in 1992, he determined they were a distinctive species.
But live birds had never been seen until this year when French nature photographer Yann Muzika was traveling in the Yenigou Valley of Qinghai province in China.
"It was a trek, not a birdwatching trip, but I was nevertheless carrying a camera and a 400mm lens, just in case," he said.
"I came across a flock of Tibetan Rosefinches (Carpodacus roborowskii) and with them there was a single bird that I did not know, resembling a Brandt's Mountain Finch but with a rufous [reddish/brown] head instead of dark brown. I took one picture before the bird flew away.
Muzika sent the photo to oriental bird expert Krys Kazmierczak.
When I saw the excellent photo of the mystery bird my immediate thought was Sillem's Mountain Finch! However, being of a cautious disposition I did quite a bit of checking and consultation with others," Kazmierczak told the BBC.
"Now we are pretty sure that it is Sillem's Mountain Finch, especially since it has been endorsed by Kees Roselaar, who simply said: 'Fantastic! At last the proof that sillemi still exists'."