Teen Who Suffered Traumatic Brain Injury Crosses 5K Finish Line

— -- A teen who collapsed and suffered a traumatic brain injury last year at a half marathon in Virginia finally completed his goal by walking across the finish line last Sunday.

Greg Kenney Sr., father of 18-year-old Greg Jr., told ABC News he and his son had been training together to compete in the Rock 'n' Roll Half Marathon in Virginia Beach last September. He had no idea that when his healthy son collapsed near the 12-mile point he would eventually be told by several doctors that his son would live in a vegetative state for the rest of his life.

The teen's mother, Stephanie, a retired chief master sergeant in the Air Force, said doctors still can't explain exactly what happened.

"Greg had just started high school. He was a senior class president. He had a 4.11 GPA. He was in the running to be the valedictorian," she told ABC News. "He worked out every day of the week. He was in perfect physical fitness when this happened. He was all set for his future."

Greg Jr. suffered a cardiac arrest on Sept. 6, 2015, while running the half marathon and suffered a traumatic brain injury due to the lack of oxygen to his brain. The Accokeek, Maryland, teen -- who was at one point in a coma, paralyzed and eating through a feeding tube -- can now eat on his own and uses a wheelchair. Because of his neurological injuries, he cannot perform most activities of daily life, according to his mother, but his speech is improving despite his vocal chords having also been paralyzed.

The young man's parents told ABC News that their son believes he will fully recover, and it's one of the reasons why he decided to participate in the 5K at this year's Rock 'n' Roll Half Marathon.

Stephanie said Greg Jr. often reminds her, "'Please don’t let people say I’m disabled. I have a temporary limitation. That’s what I have.'"

"We believe that God will restore him better than what he was before," she added. "That's the reason that this happened, was for God’s purpose."

On Sunday, Greg Sr., 55, who is also a retired member of the military, ran the half marathon.

Greg Jr. meanwhile did the 5K course in a wheelchair pushed by Jim Ryun, an Olympic silver medalist in running and a former congressional representative in Kansas. At the finish line, the teen stood up out of his wheelchair, took a few steps across, then pointed to the sky, thanking God. He hit the finish line at 1:07:20.

"It’s the highlight of my life being able to help out with this," Ryun told ABC News on Sunday. "It was an amazing moment."

Greg Sr. said his son is steadily recovering, even starting over on his senior year at a school in Clinton, Maryland.

"A lot of people never want to go back to their senior year, but he just wants to go," he said. "He's ready. He draws energy from those around him. He’s an extrovert."

Greg Jr.'s father added that his son also has dreams of performing on Broadway. "There's no doubt in my mind that that's going to happen," he said.