The world record holder in the men's marathon, 24-year-old Kenyan Kelvin Kiptum, died on Sunday in a traffic accident in Kenya.
With him in the car was his coach, Gervais Hakiziman from Rwanda, who also died.
Kiptum made a breakthrough in 2023 as a rival to compatriot Eliud Kipchoge - one of the greatest marathon runners.
And it was in Chicago last October that Kiptum broke Kipchoge's record, running 42 kilometers in two hours and 35 seconds.
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Two athletes have been selected for Kenya's marathon selection for the Paris Olympics later this year.
"Kenya has lost a special gem, this is bone-shattering news," wrote Kenya's sports minister Ababu Namwamba. on the social network Iks.
Kenyan opposition leader and former prime minister Raila Odinga said the country had lost a "true hero" and was mourning an "extraordinary person ... and an icon of Kenyan athletics".
Sebastian Coe, president of World Athletics, said Kiptum was "a great athlete who leaves an incredible legacy".
"We will miss him a lot," Kou added.
The traffic accident happened on Sunday around 23 pm local time (20 pm local time), police said, as reported by Agence France-Presse.
Giving more details about the accident, police said Kiptum was the driver and lost control of the car, which crashed.
Both Kiptum and his coach died on the spot, police added.
The spokesman, quoted by AFP, added that the third passenger - who was a woman - was injured and rushed to the hospital.
Last week, his team announced that they would attempt to run the distance in under two hours at the Rotterdam Marathon, a feat never before accomplished outdoors.
Father-of-two Kiptum's rise to fame was swift and incredible.
He only ran his first full marathon in 2022.
In his first major competition four years ago, he ran in borrowed sneakers because he couldn't afford to buy them.
He was a member of a new generation of Kenyan athletes whose career as a long-distance runner develops on the fly, unlike the previous ones who gradually transitioned to long-distance running.
Kiptum told the BBC last year that his unusual choice of career path was simply determined by a lack of money.
His coach, 36-year-old Hakizimana, was a former Rwandan runner.
Last year, he worked with Kiptum for months to break the world record.
Their relationship as a coach and athlete began in 2018, but they met when the world record holder was much younger.
"I knew him when he was a boy, he was herding cattle barefoot," Hakizimana recalled last year.
"It was in 2009, I was training near his father's farm, he would come to kick my legs and then I would chase him.
"Now I am grateful to him for what he did".