A man who was forcibly taken from his captive mother as a newborn during Argentina’s military rule and raised by strangers has been identified after 48 years, thanks to a DNA test.

The man’s sister, Adriana Metz, who had been searching for her long-lost brother for decades, said she had spoken to her sibling for the first time last week.

Ms Metz was able to find him with the help of the campaign group Grandmothers of the Plaza de Mayo, which has long tried to reunite the estimated 500 babies stolen by the military junta with their families.

Ms Metz’s brother, whose identity has not been revealed publicly to protect his privacy, is the 140th baby the group has found.

In a news conference, the founder of the Grandmothers of the Plaza de Mayo, Estela de Carlotto, read out a statement while members of the group clapped and cheered.

“Today we welcome the son of Graciela Alicia Romero and Raúl Eugenio Metz,” the 94-year-old said, while sitting next to a beaming Adriana Metz.

While the man, whom the group referred to as “Grandchild 140”, was not present, the group gave details of how he had been separated from his family.

His parents were both political activists in Bahía Blanca, a city in Buenos Aires province.

His father, Raúl Metz was one of 10 siblings. He followed in his father’s footsteps and worked on the railways, while also being an active member of the Communist Party.

His mother, Graciela Romero, studied economics and joined a Marxist guerrilla group, the PRT-ERP, with Metz shortly before the two got married.

The couple had a daughter, Adriana, and Ms Romero was five months pregnant with a second child when the two were arrested at their home in December 1976.

Shortly after seizing power in a military coup in March 1976, the junta tried to eradicate any opposition to its rule by rounding up critics.

Tens of thousands were snatched in raids and held in clandestine detention centres.

Many were tortured. Human rights groups estimate that some 30,000 people were killed or forcibly disappeared between 1976 and the end of military rule in 1983.

Survivors told the Grandmothers of the Plaza de Mayo that Graciela Romero had given birth to a son on 17 April 1977 while in captivity in the clandestine detention centre known as “La Escuelita” (Little School).

Fellow detainees say that both Romero and Metz were physically and psychologically tortured while in captivity, before being disappeared.

Their one-year-old daughter Adriana was first looked after by neighbours who eventually handed the infant to her paternal grandparents.

Both the Romero and Metz family searched for the couple and their son for decades.

The pair are listed as disappeared and are feared to be among the many left-wing activists who were killed by the military regime.

The Grandmothers of the Plaza de Mayo said it was an anonymous tip-off which had eventually led the group to “Grandchild 140”.

Working with the National Identity Commission (Conadi), an official body created to find children abducted by the military junta, they approached the man in April and offered him a DNA test.

He agreed to take the test, and on Friday Conadi informed him that he was indeed the baby snatched from Graciela Romero in 1977.

Adriana Metz said that during their phone call last week, he said that he had been raised as an only child.

“I told him ‘hey, here I am’,” she said at the press conference.

Adriana added that she was eager to meet her brother, who lives 400km (250 miles) away, in person to hug him.

Estela de Carlotto, who found her own missing grandson in 2014, said the fact that the Grandmothers of the Plaza de Mayo had managed to locate one of the missing after 48 years showed how crucial their work was even after so many decades.