"We started jogging a little bit more and he was like, 'Da, I can’t breathe,'" Dashaud told NBC Dallas-Fort Worth.
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"I was like, 'You good? Come on, we're going to get home.' And he was like, 'I can't breathe. I'm about to pass out.' And I ran to him and he fell to his knees and fell on his back," Dashaud said.
Dashaud immediately called police and emergency responders arrived minutes later, according to a GoFundMe account set up by his family. The teen was pronounced dead in his twin's arms on the way to the hospital, family said.
A statement from the Lewisville Police Department said an autopsy was underway, and there are no signs of foul play. Deshaud's family suspects cardiac arrest, even though he had been deemed in good health by a school physical earlier this year.
His mother, Razel Sheppard, called her son's untimely death "a big mystery."
"He's never been sick. He was a healthy all-around kid," she told NBC Dallas-Fort Worth. "Hopefully (we'll) get answers."
The family's GoFundMe page said Deshaud was an honor student who was working at a pizzeria to save up for a car and had dreams of one day becoming a chef.
"He was an industrious, reliable, sweet, kind and caring young man with a bright future," the page said. "He was a gentle giant, a soft-spoken brother, son, and grandson [who] loved playing football and Fortnite."
On Sunday night, dozens gathered at a Lewisville park to release red balloons in honor of the teen.
"Today our hearts are broken. Please keep the Fighting Farmer community in your prayers as we mourn the loss of a student athlete," a statement from Lewisville Football said.
Elisha Fieldstadt is a breaking news reporter for NBC News.