A man has died during an attempt to swim the English Channel as part of a gruelling triathlon.
Douglas Waymark, 44 from Cheltenham, got into difficulty about half way across, 12 nautical miles from Dover.
The coastguard received a radio call from a support vessel at about 21:20 BST on Monday.
A search and rescue helicopter arrived within 10 minutes and airlifted the swimmer to William Harvey Hospital in Ashford, but he later died.
The endurance athlete had been taking part in the Enduroman arch to arc triathlon.
'Touched our hearts'
The challenge aims to connects London and Paris by running, swimming and cycling.
Paying tribute on its website, Enduroman said: "Our friend Douglas Waymark sadly passed away swimming to France during stage two of his Solo Arch to Arc.
"He touched our hearts with his strength, organisation and quiet humour.
"He had gained massive respect amongst all who knew him. The Enduroman community will miss him and will never forget him.
"#26 will rest with Doug."
The event organiser also tweeted a picture of two t-shirts bearing Mr Waymark's name and said: "Unique T shirts made for a unique person. R.I.P Doug."
The triathlon starts with an 87 mile run from London's Marble Arch to Dover.
Then athletes must swim across the English Channel to the French coast.
Finally, they finish with a 181-mile bike ride from Calais to the Arc de Triomphe in Paris.
The Channel Swimming and Piloting Federation facilitated the swim.
Secretary Kevin Murphy said: "He was a supreme athlete, pushing himself to the absolute limits.
"He knew the dangers, but he was doing what he absolutely loved."
Mr Murphy, who has swum the channel 34 times, said everything was done to mitigate the risks.
"My understanding is that he was speaking to the people on the boat and then suddenly rolled over, inert in the water, and was pulled out.
"Everything possible was done to try and revive him.
"It happened suddenly, there was no opportunity to persuade him to come out of the water."
Mr Waymark's sister, Jo Ikel, posted a tribute on Facebook saying: "Douglas Waymark has not completed his Channel swim.
"Last night he felt he could no longer continue his quest and swam to the boat supporting him.
"He passed out and was taken by helicopter to a hospital in Ashford. At around midnight, he sadly died.
"We are all devastated but take comfort in him doing what he loved best to the very end."
Mr Waymark, who was originally from Swansea, set off from Shakespeare beach at 07:27 BST but began to struggle later in the day.
Updating followers on Mr Waymark's progress throughout, Enduroman tweeted he was given painkillers around 17:00 BST. Swimming across the tide, he missed a feed and Enduroman said "he doubts but pushes on".
The last word on his progress came at 20:30 BST, saying he was swimming on through cooling temperatures and fading light.
Mr Waymark's tracker regularly posted his position online and the last data visible between 21:09 and 21:38 BST showed he had turned around and was heading back towards Dover.
Kent Police confirmed his death is not being treated as suspicious.