Investigators say it started at Fox Meadow Apartments on Adams Drive at 10:26 p.m.
The family identified the boy as 12-year-old AJ Marles. His mom, Shannon, and 7-year-old sister, Hope, remain hospitalized.
"Alan John was the love of my life. My first biological grandson, all I wanna do is hug him," said Kim Dupell, the boy's grandmother. She says he loved video games, his family, and his dog.
Classmates of AJ, a sixth-grader, told Action News that the news of his death was discussed at school on Monday.
"We're just talking about how he didn't survive, and it was a lot going on, counselors coming in," said Milania Wheeler, a sixth-grader from Maple Shade.
As dozens of families deal with the aftermath, the Maple Shade Business Association is hoping to help. It opened two donation accounts at Columbia Bank for victims -- one for the families displaced and another for the Marles family.
"Obviously they have nothing left, so anything anyone can donate will be greatly, greatly appreciated," said Dupell.
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Several other injuries were reported in the blaze, though none are said to be serious.
Viewer video showed intense flames burning through the roof at the Fox Meadow apartment complex.
"I looked out the window and I saw this light and I thought, 'Oh fireworks. Those are really powerful fireworks. Oh that's not fireworks,'" recalled Zachary Patchell of Maple Shade.
Firefighters blasted water at the flames trying to get the upper hand.
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A total of 16 units were damaged.
Officers immediately began evacuating people, while firefighters worked to put out the blaze.
Firefighters from Maple Shade as well as a number of other communities responded.
The fire was placed under control around 11:40 p.m.
The Marles family was part of an Action News investigation last year into Fox Meadow Apartments. They helped uncover hundreds of violations at the complex.
The cause of this fire is under investigation.
"All the neighbors were knocking, banging on our door. Boom, boom, boom, boom. Let's go, let's go. So by the time we got out, it spread," described resident Hyacina Wertz.
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SEE ALSO: Troubleshooters: South Jersey apartment complex cited with hundreds of violations
Troubleshooters: South Jersey apartment complex cited with hundreds of violations
Action News has reached out to the apartment complex for comment but we have not heard back.
The Red Cross of New Jersey says a total of 22 families were displaced, and they are providing assistance for temporary lodging, food, and clothing for 12 of those families.
Darwin Adad is among the dozens of residents who can't get into their homes.
"We need some help because we're in the street now. My family, me, we don't have anything right now," he said.
"You can see through my apartment to the back door. My belongings, you know what I mean, are just sitting there," added Arlene Johnson who also lives in the complex.
The state and county fire marshals are among the offices investigating.