William Dunlop has passed away after an incident during practice for the Skerries 100 road races in Ireland.
Southern 100 club chairman George Peach described the 32-year-old as such a likable rider who always had a smile for everyone.
The tragedy is the third racing fatality suffered by the Dunlop family, with Joey killed in a crash in Estonia in 2000, while William's father Robert lost his life following a crash during practice for the 2008 North West 200.
Dunlop recently revealed he was expecting a second child with his partner Janine. Joey Dunlop still holds the record of most Isle of Man TT wins, with an astounding 26.
Tributes have poured in for Dunlop, who secured 108 Irish National Road Race wins during a distinguished career.
Also speaking at the Co Donegal golfing event, host Rory McIlory said: "I think it's unfortunate, what the family have been through has been horrendous".
"It is devastating news that William has also lost his life so tragically and my thoughts and prayers and those of the people of this Council area, are with the Dunlop family at this very hard and sad time".
DUP leader Arlene Foster said she was "shocked and saddened" by the racer's death.
Motorcyclist Carl Foggarty said that his thoughts were with William's family.
"Motorcycling was his life and he will be forever remembered for his many achievements, both in Ballymoney and across the world", she tweeted.
"A man in his 30s was fatally injured in a crash", a garda spokesman has confirmed.
Dunlop made no secret of his love for the Dundrod course at the Ulster Grand Prix and it was here where William's class really shone through.