The Duke of Cambridge and Prince Harry have expressed their immense sadness at the death of explorer Henry Worsley, who was on the brink of making history with the first solo crossing of the Antarctic.
The ex-Army officer, 55, from Fulham, south-west London, was just 30 miles (48km) from becoming the first adventurer to cross the continent unsupported and unassisted when he had to call for help and was airlifted off the ice on Friday.
He was flown to a hospital in Punta Arenas in Chile, where he was found to have bacterial peritonitis. He underwent surgery but died on Sunday.
Worsley was trying to complete the unfinished journey of his lifelong hero Sir Ernest Shackleton to mark the 100th anniversary of Shackleton's expedition.
The trek was raising money for the Endeavour Fund, a charity which helps wounded servicemen and women and is managed by the Royal Foundation of The Duke and Duchess of Cambridge and Prince Harry.
William, who was patron of the expedition, said he and Harry had lost a friend as he paid tribute to Worsley's ''selfless commitment'' to fellow soldiers.
Fellow adventurers Bear Grylls and Ben Fogle described their devastation at hearing the news. Grylls wrote: "One of the strongest men & bravest soldiers I know. Praying for his special family," while Fogle said: "So sad to hear that Antarctic explorer Henry Worsley @shackletonsolo has passed away. An inspiration to us all."
Battling temperatures of minus 44C (minus 47.2F), tackling white-out blizzards and treacherous ice, the former-lieutenant colonel was 71 days into his expedition, had passed the South Pole and covered 913 miles (1,469km).
After spending two days unable to move from his tent, the married father-of-two took the decision to pull out of the charity adventure after suffering from exhaustion and severe dehydration.
His wife Joanna, who flew to be by his side, said in a statement: "It is with heartbroken sadness I let you know that my husband, Henry Worsley, has died following complete organ failure; despite all efforts of ALE (Antarctic Logistics and Expeditions) and medical staff at the Clinica Magallanes in Punta Arenas, Chile."
She paid tribute to her husband for reaching his goal of raising more than £100,000 to help wounded service personnel.
"Henry achieved his Shackleton Solo goals of raising over £100,000 for the Endeavour Fund, to help his wounded colleagues, and so nearly completing the first unsupported crossing of the Antarctic landmass," she said.
"A crossing made, under exceptionally difficult weather conditions, to mark the 100th anniversary of Sir Ernest Shackleton's Endurance expedition - his lifelong hero.
"On behalf of myself and family, I wish to thank the many hundreds of you who have shown unfailing support to Henry throughout his courageous final challenge and great generosity to the Endeavour Fund.
"Donations now total over £106,773."
William and Harry pledged to ensure Worsley's family, which includes his two children, Max, 21, and Alicia, 19, received the help they needed in the wake of his death.
"Harry and I are very sad to hear of the loss of Henry Worsley. He was a man who showed great courage and determination and we are incredibly proud to be associated with him," the Duke said.
"Even after retiring from the Army, Henry continued to show selfless commitment to his fellow servicemen and women, by undertaking this extraordinary Shackleton solo expedition on their behalf.
"We have lost a friend, but he will remain a source of inspiration to us all, especially those who will benefit from his support to the Endeavour Fund.
"We will now make sure that his family receive the support they need at this terribly difficult time."
William had waved Worsley off from Kensington Palace in October, ahead of the start of the trek, and sent him a Christmas message, telling him how proud everyone was of him.
Peritonitis occurs when the thin layer of tissue lining of the abdomen becomes infected. Symptoms can include swelling of the abdomen, vomiting, chills, lack of appetite and a high temperature. Complications include sepsis and septic shock.
In his final statement sent from Antarctica, Worsley described how his desire to help wounded soldiers with their rehabilitation was the central focus of his expedition, but that he had taken the decision to call for help.
"The 71 days alone on the Antarctic with over 900 statute miles covered and a gradual grinding down of my physical endurance finally took its toll today, and it is with sadness that I report it is journey's end - so close to my goal," he said.