Two runners have died after competing in Sunday's Cardiff Half Marathon, police and organisers have confirmed.
The pair, aged 25 and 32, went into cardiac arrest after crossing the finishing line.
About 20,000 people took part this year - which was the race's 15th anniversary.
Run 4 Wales chief executive Matt Newman said: "This is a terrible tragedy for the families. Our deepest sympathies go out to their family and friends."
He added: "Everyone connected with the race is devastated.
"They unfortunately become the first fatalities in the 15 year history of the race."
The men were treated on the finishing line before being taken to Cardiff's University Hospital Wales.
South Wales Police said the men's next-of-kin had been notified.
This year's event got under way at 10:00 BST outside Cardiff Castle.
Participants ran via the Wales Millennium Centre, the Cardiff Bay Barrage as well as Roath Park
Australian runner Jack Rayner won the race, crossing the line in 1:01:01 and Dewi Griffiths was the first Welshman to finish.
Uganda's Juliet Chekwel won the women's race in 01:09:45 to become Commonwealth champion.
The race is now the UK's second largest half marathon behind The Great North Run.
Officials said this year's event was the biggest yet and could be worth more than £2.3m to the local economy.
The half marathon is also the biggest fundraising event in Wales - with 800 charities, such as the NSPCC, benefitting from the runners' sponsorship money.