The attack was reportedly so savage that the lad's face was ripped off by the big cat's claws and teeth.
Police in Para state, northern Brazil, are now investigating Dierlissom Oliveira Paiva's death in a rural area near Brasil Novo, in the Brazilian Amazon.
The schoolboy disappeared on Wednesday afternoon (July 27) after going out to fish in a pond in a forested area.
After he failed to return home, his dad and neighbours went out to look for him.
But when they arrived at the pond, they found items of clothing and traces of blood on the ground.
A little over 50 metres away, they found the youngster's body with his face completely disfigured.

The suspicion is that he was brutally savaged by a jaguar, with locals reporting that jaguar sightings are common around the pond.
In a statement, the Civil Police said: "According to witnesses, close to the body there were large animal paw prints and signs of a possible jaguar attack."
There were also reportedly signs the body had been dragged.
According to some reports, following the boy's death, locals went out and hunted the big cat responsible in revenge.
The animal - an extremely rare black jaguar - was allegedly found with a deep cut in to its neck.
Other reports, however, stated that no animal had been found nearby.
The child and his family had reportedly been living in the rural community for just six months.
The boy's aunt, who chose to remain anonymous, told local media: "He was very close to us, a very happy boy."
A 2015 report said around 600 black jaguars were thought to exist in the wild.
The investigation is ongoing.
It comes after a 14-year-old boy narrowly escaped having his leg torn off by a jaguar after the predator latched onto his leg when he crossed a security barrier at a zoo.




Move over humanity. There are other peoples on this planet, and 'they' eat 'your' kids, too...
My sincere condolences. My infant cousin was attacked by our Husky Malamute (canidae carnivora) crossbred with Wolf (canis lupus carnivora). That was it for me...