Alex Batty, from Oldham, Greater Manchester, was 11 when he failed to return from a family holiday to Spain with his mother and grandfather in 2017.
He has now spoken out for the first time, having been reunited with his grandmother and official guardian, Susan Caruana, in the UK.
Here is everything we know about what happened to Alex.
How did he go missing?
Ms Caruana has previously said Alex’s grandfather and mother had taken the child abroad to live an “alternative lifestyle”, possibly in a spiritual commune in Morocco.
She told the BBC: “They didn’t want [Alex] to go to school, they don’t believe in mainstream school.”
Both his mother and grandfather – Melanie Batty, then 37, and David Batty, who was 58 – were forbidden from being with the boy because of domestic difficulties.
An investigation was launched on 8 October 2017 after the three of them never returned from a holiday in Marbella.
French investigators said he was found earlier this month after days of hiking, escaping from a rural community in the Pyrenees.
How was he found?
Alex, now 17, was picked up by chiropody student Fabien Accidini near the French city of Toulouse in the early hours after the teenager was walking alone across the Pyrenees “for four days and four nights”, with only a backpack and skateboard.
The driver reportedly called the police after speaking to the boy at length and becoming suspicious.
The chiropody student, speaking to a reporter at local newspaper La Dépêche, said Alex had been “living in a kind of itinerant commune” with his mother.
Why did he leave his mother?
In his first interview since returning to the UK, Alex said he no longer wanted to live with his “anti-government, anti-vax” mother after an argument, saying she was “a great person but not a great mum”.
Alex told The Sun he thought to himself after an argument with his mother “I’m gonna leave because I can’t live with her”.
The teenager said he had become fed up with his nomadic lifestyle with “no friends” and “no social life”, with little possibility to work or study.
He told the newspaper the only friend he had been able to make was a Spanish girl he met in a café.
“I realised it wasn’t a great way to live for my future,” he said.
Where is Alex now?
After being looked after by the French authorities, Alex is now back in the UK under the legal guardianship of his grandmother in Oldham.
“Being back with my grandma feels quite surreal,” Alex said. “I feel like I’m going to be waking up back in France. It’s not really kicked in yet that I am back in England.
“I was driven back to my gran’s house and I walked in the door and she’s in the living room. I started shaking and just gave her a massive hug.
“The house is different now but still feels the same.”
His grandmother said last week that it was “so good to hear his voice and see his face again”.
In a statement issued through Greater Manchester Police, she said: “I cannot begin to express my relief and happiness that Alex has been found safe and well.”
Last week, French prosecutors said the teenager’s mother may now be in Finland.