Organisers of the Virgin Money London Marathon have confirmed 29-year-old professional chef Matt Campbell died after collapsing during yesterday's event.
Campbell, from the Lake District, received "immediate" medical attention after collapsing at the 22.5 mile mark of the mass participation race.
He later died in hospital.
The cause of death has not been revealed.
Campbell was a well-known chef having featured in the television competition show Masterchef: The Professionals last year.
He was running for The Brathay Trust, a national charity, that provides life changing programmes for children and young people, and in memory of his father, Martin, who died in the summer of 2016.
Organisers joined his family in paying tributes to their "inspirational son and brother", a keen marathon runner and who had completed the Manchester Marathon in under three hours earlier this month.
Campbell posted on Twitter that yesterday was his second marathon in a fortnight.
"Our thoughts go to his family and friends at this sad time," race director Hugh Brasher said here today.
"It is unusual when it happens but it is always tragic.
"There will be an autopsy done and we should not speculate [on the cause]."
Yesterday's event took place amid temperatures of 23.2 degrees Celsius, a record high for the London Marathon.
Those in the mass participation races, a staple of the event, experienced the warmest weather as they took to the course later than athletes in the elite competitions.