Mountaineers said the Hillary Step may have fallen victim to Nepal's devastating 2015 earthquake.
The near-vertical 12m (39ft) rocky outcrop stood on the mountain's southeast ridge, and was the last great challenge before the top.
It was named after Sir Edmund Hillary, who was the first to scale it in 1953.
British mountaineer Tim Mosedale confirmed the news of the Step's demise on Facebook after reaching the summit on 16 May.
Speaking to the BBC, he said the loss of the Step was "the end of an era".
"It is associated with the history of Everest, and it is a great shame a piece of mountaineering folklore has disappeared," Mr Mosedale said.
Back in May 2016, pictures posted by the American Himalayan Foundation appeared to show that the Hillary Step had changed shape.
But thanks to the snowfall, it was hard to tell for sure. This year, with less snow, it was clear the Step had gone.