Marquel's aunt, Nicole Alexander, told WJRT on Monday that doctors said the infection traveled to her nephew's brain.
“The doctor came in and said, ‘He has a sinus infection. It has penetrated through the bone into the blood vessels in the brain and we see some blood clots,’” said his aunt, Nicole Alexander.
Gilbert said Marquel had two strokes and went to an Ann Arbor, Michigan, hospital for surgery.
“It takes a long time to get blood clots to shrink and the blood clots were putting too much pressure on the brain and he couldn’t get proper oxygen to his brain,” Alexander said.
The eighth-grader died Sunday.
"He was my favorite person. Now, he's not gonna be here anymore," Marquel's sister Alexandria Brumley said, according to WNEM. "I feel like it's not real. I feel like he's gonna come back. But I know he's not gonna come back."
Gilbert set up a GoFundMe page to help Marquel's family with expenses. It has raised more than $5,000 of its $10,000 goal.