British teen Alex Batty is due back in the UK in the next few days, after he was found in France having been missing for six years, police said.
The 17-year-old vanished in 2017 on a holiday in Spain with his mother and grandfather.
His family in the UK is "massively relieved" and going through a "whole host of emotions", Greater Manchester Police (GMP) said.
Its priority was his safe return to the UK, the force said.
He was found on Wednesday morning by a motorist close to Toulouse in the south of France.
Chris Sykes, assistance chief constable of GMP, said the force was "relieved and overjoyed" to receive the news that Alex is safe and well.
"This is a huge moment for Alex, for his family and for the community in Oldham," he said in a press conference.
"The young man and Alex's grandmother spoke on a video call last night and whilst she is content that this is indeed Alex, we obviously have further checks to do when he returns to the United Kingdom," he said.
He added that the force's main priority is now to see Alex return home.
"We still have some work to do in establishing the full circumstances surrounding his disappearance and where he has been in all those years," he said.
He added that Alex's mother - who does not have parental guardianship of him - is "part of" the investigation. Her whereabouts are unknown.
A police source earlier told OceanNewsUK the boy had been taken to a police station by a concerned motorist who had spotted him on a road in the foothills of the Pyrenees early on Wednesday morning.
"He explained that he had been walking for four days, that he set off from a place in the mountains, though he didn't say where," delivery driver Fabien Accidini said.
"I typed his name into the internet and saw that he was being looked for," he said.
Mr Accidini told local media the teenager's plan had been to find a big city with an embassy to ask for assistance. Instead, Mr Accidini contacted French authorities for help.
He added that they talked for more than three hours, in which Alex told him his story.
The delivery driver said he lent the teenager his phone and let him use his Facebook account to contact his grandmother, Susan Caruana, who is also his legal guardian.
His first words to his grandmother for six years were: "Hello Grandma, it's me Alex. I'm in France Toulouse. I really hope that you receive this message. I love you, I want to come home."
It is understood that Alex had been living in the remote Pyrenean valleys, travelling about from place to place in a kind of itinerant commune.
The area in the foothills of the Pyrenees is known for attracting people in search of alternative lifestyles.
Alex, from Oldham in Greater Manchester, will not say where his mother is or exactly where he had been living in the Pyrenees, the prosecutor's office told the OceanNewsUK.
Ms Caruana told the OceanNewsUK in 2018 that she believed Alex's mother Melanie Batty and grandfather David Batty had taken him to live with a spiritual community in Morocco.
She said at the time they were seeking an alternative lifestyle and did not want Alex to go to school.
Melanie and David Batty left Greater Manchester with Alex for a pre-agreed week-long holiday to Marbella in Spain on 30 September 2017.
He was last seen at the Port of Malaga on 8 October that year, the day they were expected to return to the UK.
British police were contacted via the UK embassy in Paris.
In a statement, the Foreign, Commonwealth and Development Office (FCDO) said: "We are supporting a British national in France and are in contact with local authorities."
