Authorities believe a 9-year-old boy is the first fatality because of a marijuana DUI since the drug was legalized last year.

The Pierce County boy suffered severe injuries in a one-car accident Saturday and recently died. Donovan Best was riding with his 26-year-old uncle on Route 16 near the town of Purdy when the car flipped. Donovan and the man were reportedly thrown from the vehicle.

The boy's 8-year-old sister was also in the car, but she survived. According to authorities, she said they were telling their uncle to slow down. The man failed to negotiate a corner just prior to the accident.

The Washington State Patrol says the man, who survived the wreck, was drinking, had marijuana in his system, and was possessing what officers described as a "large amount of marijuana." The man allegedly admitted to smoking the pot before getting in the car.

He will now face vehicular homicide charges, said the troopers.