Social services and police freed Ilko Todorov after a tip-off from neighbours who claimed they saw him tied to a long steel chain by his leg in the family home in the town of Goce Delchev, Bulgaria.
The chain, attached to his leg, only allowed him to move though a limited space in the house and is reported to have caused injuries.
Ilko Todorov was shackled "like a dog" each morning before his parents went to work.
"They kept him like a dog," The Sun quoted neighbour Nikifor Ivanov, as saying.
Ilvo's dad Ilija, 40, a metal worker, and mum Marija, 34, face cruelty charges.
Ilko, speaking at a foster home, said: "I'm happy here. I miss my mum, but not my dad."
Cleaner Marija blamed her partner, saying she was afraid of him.