The 28-year-old was bitten in the leg in the ocean at Pointe au Sel, Reunion on Saturday morning.
Dubosc was dragged to the shore but the emergency workers were unable to rescue him.
A police spokesman said: “The young man was in the water with two friends, when a shark attacked him, biting his right thigh, and his groin area.
“The victim was pulled out of the water, and emergency workers arrived very quickly. Despite cardiac massage, he died within half an hour of the attack.”
Just weeks earlier, his best friend Alexandre Naussac died after being mauled by a shark on a nearby beach.
Dubosc is the ninth person to be killed in a shark attack off Reunion in the last six years.