The men's marathon world record holder, Kenya's Kelvin Kiptum, has died in a road accident in his home country.
He was travelling in a vehicle on a road near the town of Eldoret, close to where he had been training the BBC reports.
The 24-year-old Kiptum emerged in 2023 as a rival to his compatriot Eliud Kipchoge.
He broke Kipchoge's world record in Chicago last October, running the 26.1 miles in two hours and 35 seconds.
Just last week, his team announced that he would attempt to run the distance in under two hours at the Rotterdam marathon - a feat that has never been achieved in open competition.
Kenya's opposition leader and former prime minister, Raila Odinga, said on X that the country had lost "a true hero" and was mourning "a remarkable individual... and Kenyan athletics icon".
Paying tribute to the young man, Sebastian Coe, the president of World Athletics, described Kiptum as "an incredible athlete leaving an incredible legacy, we will miss him dearly".
The rise to fame for the young father-of-two had been rapid - he only ran his first full marathon in 2022.
He competed in his first major competition four years earlier running in borrowed shoes as he could not afford a pair of his own.
He was among a new crop of Kenyan athletes who began their careers on the road, breaking away from the past tradition of athletes starting on the track before switching to longer distances.
Kiptum told the BBC last year that his unusual choice was simply determined by a lack of resources.
"I had no money to travel to track sessions," he explained.