Austin Clark Norman, 18, killed, Brandon Douglas Norman, 17, injured, taken to hospital, after their pickup leaves an unpaved county road and crashes into a tree near Middleburg.

An 18-year-old was killed and his 17-year-old brother was critically injured in a single-vehicle crash Sunday evening on an unpaved Clay County road.

Brandon Douglas Norman, 17, was driving a black Toyota Tacoma pickup truck on Louie Carter Road just before 7 p.m. He lost control on a muddy, dirt road, and the pickup left the road and struck a tree, according to the Florida Highway Patrol report. Troopers said the brothers were test driving the 1992 pickup that had recently been purchased by their family when they crashed.

Troopers said the brothers' father found them and their truck after he went searching for them because they hadn't returned.

Norman was flown to UF Health Jacksonville with critical injuries. Austin Clark Norman, 18, was a passenger in the truck and died at the scene.

Neither of the teenagers was wearing a seat belt, according to the FHP report.

The Normans' grandmother talked on Monday morning about the teens. She said they've always been such a joy to her and she can't believe Austin is gone.

"(Austin) never did drugs, never drank. Loved to go fishing," Marsha Norman said. "That and hunting was his two hobbies he loved so good. Loved to work, enjoyed going to school. He wanted to be an RN to help people and go back to be a pediatrics doctor to help little children."

She said the teens worked hard to help their dad, who was a single parent. Brandon recently got hired at a new Chick-fil-A in Middleburg, and Austin worked at Russell's Feed for the last two years.

Norman said the boys' friends have been coming out to support the family since the crash.

Norman said Brandon was scheduled to undergo surgery on Monday morning. He has a broken femur and broken ankle.

Doctors planned to do surgery on his leg and may have to wait on the ankle because of the swelling. He also has a cracked sternum, but his family expects him to be OK.

The Normans are still trying to figure out what caused the crash.

"The police told my son they don't know how it happened. There was no skid marks," Norman said. "The last neighbor saw him go by the house and he wasn't running very fast and don't know how the crash had such an impact unless the little truck got away from Brandon driving it."

According to the Middleburg High School principal, Brandon was a senior at the school and Austin graduated in 2013.

On Monday morning, Clay County schools issued a statement: "Our thoughts and prayers go out to the family during this difficult time. The district has a team of grief counselors on site."