Eddie Izzard has been forced to abandon his attempt to run a marathon every day for 27 days due to "medical complications".
The comedian said he was "very sorry to let everyone down" as he announced the tough journey was on hold.
Izzard had finished four of the 26-mile runs when he was forced to quit his unusual tribute to former South African president Nelson Mandela.
But he said he will return to complete the punishing challenge in the future.
In an online message to his fans today, he said: "I set out to run 27 marathons in 27 days as a tribute to Nelson Mandela and his 27 years spent in prison.
"Having completed four marathons, unfortunately, I have had to put my attempt on hold due to unforeseen medical complications that have arisen due to a multitude of factors including severe terrain, humidity and altitude.
"But I wish to say that my attempt is not over and I will return to South Africa and run the 27 marathons and finish this story."
He added: "I owe that to Nelson Mandela, who has inspired the world to struggle and succeed no matter what obstacles are thrown at us."
During his South African challenge, he was also filming a documentary about Mandela, visiting some of the key locations in his life. Money raised from his feat was to be used to help disadvantaged people in the country.
After his third marathon of this challenge he wrote online that it was "maybe
the hardest I've ever run".
In 2009, Izzard completed 43 marathons in 51 days for Sport Relief.