Boyan Petrov, 45, had scaled 10 of the world’s 14 highest peaks of over 8,000 metres in the Himalayan and Karakoram mountains solo and without supplementary oxygen.

Members of Petrov’s team last saw him alive by telescope on May 3 at 7,500 metres.

He is considered to have been missing since May 5 when other team members, who were a day behind him, found his tent empty at the last camp before the summit.

The Tibetan peak is the 14th-highest in the world.

A joint search was launched by Chinese mountain rescuers and a Nepalese helicopter rescue team.

“We call the search over. Boyan is a legend. All of Bulgaria thanks you. This is the end,” Kiril Petkov, a friend and member of Petrov’s team, said in a message on Facebook.

Petrov, who was also a prominent zoologist, had previously battled cancer and was an insulin-dependent diabetic.

Two years ago he was left in a coma after being struck by a car while researching wildlife in southwestern Bulgaria.

He had planned to scale Mount Everest on his next expedition, aiming to become the 20th person to have conquered all 14 peaks over 8,000 metres without oxygen by 2019.