One of the support team for the Amgen Tour of California died during stage 4 at a remote mountain sprint on the Pacific Coast Highway.
Cyclingnews witnessed medical attention being given to Rob Llewelyn, one of the several motorcyclists who accompany the race, at the first KOM point, 72km into the 215km stage from Morro Bay to Laguna Seca Raceway.
Initial reports in American outlets suggested that the driver lost consciousness and crashed, but the TV Motos International organisation issued a statement saying he was parked when he suffered "an apparent heart attack".
Organisers of the Tour of California have since issued a statement saying, "Today the sport of cycling, NBC and TV Motos International and Amgen Tour of California lost a friend when television moto pilot Rob Llewelyn suffered a fatal heart attack while standing on the side of the road waiting for cyclists to approach his position. Rob was a 20-year veteran driver who was passionate about the sport. A moment of silence was observed at the start of both the men's and women's races in memorium."
The TV Motos International organizations went on to say, "It was a beautiful day, but, ultimately, a truly sad day, which will be remembered for the passing of a great friend and colleague, Rob Llewelyn," read a statement on the TV Motos International Facebook page.
"Rob passed away today during Stage 4 of the race from an apparent heart attack, while parked with his moto on this stretch of the California coast.
"Rob will be remembered always and profoundly missed. Our deepest sympathies go out to his family."
This article was updated at 18:00 GMT on 19/05