The 44-year-old climber from Birmingham, England, “suddenly fell down” during his climb down, according to Murari Sharma, a spokesman for Fisher’s expeditionary company.

“Our sherpa Jangbu tried to wake him up and change his oxygen bottle and tried to give him some water but there was no response,” said Sharma, who added the sherpa was also complaining of sickness before being rescued.

“My heart is broken,” wrote Fisher’s partner, Kristyn Carriere, on Facebook. “It was his ultimate challenge.”

The death toll for climbers on Himalayan mountains this season has now hit 20, according to the Himalayan Times.