Sir Ranulph Fiennes was today forced to abandon his bid to conquer Mount Everest after succumbing to exhaustion.
The multi-million pound charity climb was the adventurer's second unsuccessful attempt at scaling the mountain — he suffered a heart attack just 300m from the top in 2005.
Having set off from base camp on Tuesday, Sir Ranulph had reached the final stopping off point in the ascent after traversing the "death zone", but had to turn back before reaching the 8,850m summit.
The 64-year-old explorer, who recently underwent an operation for prostate cancer, once again had to contend with heart problems and vertigo, a spokesman said.
Sir Ranulph has now begun his descent to Base Camp after resting at Camp 4. Accompanying him are expedition guide Kenton Cool and medic Robert Casserley.
The group took the south Col route up the mountain from Nepal, first climbed in 1953 by Sir Edmund Hillary and Tenzing Norgay.
They hope to raise £3 million for cancer charity Marie Curie — close to £2 million has already been pledged.
The Olympic torch relay, which was being carried to the summit, delayed the group at the start of May as restrictions were imposed on other climbers.
Sir Ranulph's other feats include reaching both poles, crossing the Antarctic and Arctic Oceans, leading the first hovercraft expedition up the Nile and running seven marathons in seven days on seven continents.