Yorkshire rider James Cowton has been killed at the Southern 100 road races at the Isle of Man.
Cowton, 26, was involved in a four-rider bike accident at Stadium Bends and succumbed to his injuries.
Lincolnshire's Ivan Lintin, who sustained critical injuries in the crash, has undergone a leg operation.
The other two riders involved in the incident, James Coward and Mickey Evans, were discharged from hospital on Friday.
"The Southern 100 MCRC regret to announce that following an incident involving four competitors at Stadium Bends during the 600cc Challenge race, Driffield rider James Cowton succumbed to his injuries," said a statement from the organisers.
"Southern 100 Racing extends its sincere condolences to family, relatives and friends of James Cowton at this very sad time.
"The organisers are carrying out a full investigation in conjunction with Isle of Man Constabulary into the circumstances of the incident on behalf of the Coroner of Inquests."
Cowton won the 250 Lightweight race at the 2014 Ulster Grand Prix, his maiden international road race success, and also claimed his first North West 200 win for Northern Irish outfit McAdoo Racing in May's second Supertwin race.
He had also won three races at the Southern 100 in previous years, with victory at this year's Supersport race at the Cookstown 100 another highlight.
Lintin, a Supertwin specialist, is also a regular on the international road racing scene, and has two Lightweight victories at the Isle of Man TT, as well as two North West 200 and three Ulster Grand Prix wins in the class.
A statement from Lintin's team, Dafabet Devitt Racing, said: "Ivan was involved in the incident in the final race at the S100.
"Ivan is in a critical condition and has been flown to Liverpool for further treatment. Thoughts are with James' family at this time and also Ivan's close friends and family."
Tom Robinson, from North Yorkshire, was critically injured after crashing during practice for the 600cc Supersport class on Monday night.