Alice Brown told the paper that her grandson had asthma and was not a smoker, but he'd heard a certain type of vape pen could help with his condition.
When William got out of the store, he chose to use his vape pen in his vehicle, which is when it combusted.
"He popped it and it exploded, and that's when it shot across his mouth", Alice Brown told the station.
His family said doctors took X-rays and knew Brown had a piece of e-cigarette lodged in his throat and put him in a medically-induced coma, but never operated on him. "I miss him already, and knowing he won't open that door and come through it ever again is the hardest part".
The vape store - Smoke and Vape DZ - refused to comment to WFAA about the incident. "It's a waste of the things he could have accomplished", Alice added.
She continued: "It just all seems so unreal".
It's unclear what company created the vape pen in question. "That three-piece thing went into his throat and stayed there", she continued.
A FEMA report published in 2017 listed 195 incidents of explosions or fires caused by e-cigarettes between January 2009 and December 2016.
Brown is believed to be only the second person to die in the US from an exploding vape pen.
Firefighters could not determine the cause of death, but the Pinellas-Pasco Medical Examiner's report made it clear that two pieces of the smoking device had penetrated his cranium, resulting in his death. The study said there were likely more injuries that went unreported.
William Eric Brown died after his e-cigarette exploded.
In May, a 38-year-old Florida man was killed when his vape pen exploded, ejecting shrapnel into his face.
He also suffered burns on about 80 percent of his body.
Electronic cigarettes, or vape pens, are battery-operated devices that heat a liquid to generate vapor - which may contain nicotine - that users can inhale.