Cheptegei, 33, who competed in the marathon at the Paris Olympics, suffered burns to more than 75 per cent of her body in the September 1 attack and died four days later.
Her former boyfriend, Dickson Ndiema Marangach, died on Monday night, said Daniel Lang'at, a spokesperson at Moi Teaching and Referral Hospital in Eldoret in western Kenya, where Cheptegei was also treated and died.
"He died from his injuries, the burns he sustained," Lang'at told Reuters.
Local media reported he had suffered 30 per cent burns when he assaulted Cheptegei as she was returning home from church with her children.
Ndiema and Cheptegei were said to have quarrelled over a piece of land the athlete bought in Kenya, according to a report filed by the local police chief.
The athlete's father, Joseph Cheptegei, told reporters last week that Ndiema was stalking and threatening her and the family had informed police.
Cheptegei, who finished 44th in Paris, is the third elite sportswoman to be killed in Kenya since October 2021.
Her death has put the spotlight on domestic violence in the East African country, particularly within its running community.
Rights groups say female athletes in Kenya, where many international runners train in the high-altitude highlands, are at a high risk of exploitation and violence at the hands of men drawn to their prize money, which far exceeds local incomes.
"Justice really would have been for him to sit in jail and think about what he had done. This is not positive news whatsoever," said Viola Cheptoo, co-founder of Tirop's Angels, a support group for survivors of domestic violence in Kenya's athletic community.
"The shock of Rebecca's death is still fresh," Cheptoo told Reuters.
Cheptoo co-founded Tirop's Angels in memory of Agnes Tirop, a rising star in Kenya's highly competitive athletics scene, who was found dead in her home in the town of Iten in October 2021, with multiple stab wounds to the neck.
Ibrahim Rotich, Tirop's husband, was charged with her murder and has pleaded not guilty. The case is ongoing.
Nearly 34 per cent of Kenyan girls and women aged 15-49 years have suffered physical violence, according to government data from 2022, with married women at particular risk.
The 2022 survey found that 41 per cent of married women had faced violence.
Globally, a woman is killed by someone in her own family every 11 minutes, according to a 2023 UN Women study.
Cheptegei is expected to be buried at her home in Uganda on Saturday.
with AP
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