Argentine activist Maria Isabel Mariani, known as Chicha ,who spent nearly half of her life looking for her missing granddaughter will need to resume her search after a case of mistaken identity.

Chicha Mariani, 92, announced on December 24 that she had finally met her granddaughter.

Clara Anahi Mariani Teruggi was abducted by the military in 1976.

But a prosecutor working on the case said Chicha Mariani had been introduced to the wrong woman.

The announcement on December 24 was hailed as another triumph for the campaign group Grandmothers of the Plaza de Mayo, which was formed to reunite families with their missing children.

Even President Mauricio Macri celebrated the news on his Twitter account. He tweeted: “I want to wish Chicha Mariani, her granddaughter, and all the family a happy Christmas reunion.”

On December 26, DNA tests were released showing that the woman Chicha Mariani met was not her missing granddaughter.

“There is no genetic match between Ms Mariani and her alleged granddaughter,” said prosecutor Pablo Parenti, Head of the Attorney General’s Unit for Cases of Child Appropriation.

Chicha Mariani founded her own organization, the Anahi Foundation, which includes one of her granddaughter’s names, after stepping down as president of the Grandmothers in 1989.

Results from an official bank of genetic samples were negative.

Chicha Mariani, who is nearly blind, is devastated, said Anahi Foundation spokesman Juan Martin Ramos Padilla.

“It was a hard blow for Chicha,” he said, adding that she is determined to carry on.

“She is 92 and will continue searching for her granddaughter. We just hope to be able to find her.”

Chicha Mariani’s granddaughter was abducted 39 years ago at just three months old.

Her parents, Daniel Mariani and Diana Teruggi, were members of the Montoneros left-wing group.

The baby was taken from their home in an operation in which Diana Teruggi was killed.

Chicha Mariani’s son, Daniel, escaped but went into hiding and was killed a few months later.

There is no suggestion that the woman who met Chicha Mariani had attempted to deceive her. The Buenos Aires Herald identified her as Maria Elena Wehrli.

Maria Elena Wehrli arrived at Chicha Mariani’s house on Christmas Eve with the results of a DNA test carried out by a private laboratory,” said prosecutor Pablo Parenti.

“The National Genetic Database is the only body authorized to determine the identity in these cases,” he added.

The Grandmothers encourage children who were born during the military government, between 1976 and 1983, and have any doubts over their identity to come forward and do a DNA test.

The organization has already reunited 119 children to their families, the most recent last month.

Most pregnant women arrested by Argentina’s secret police were killed shortly after giving birth.

Some 500 children were abducted from their mothers in captivity.

They were often given for adoption for non-communist families. In other cases they were just handed over to orphanages.

Some of the adoptive parents knew of their children’s backgrounds, but many of them did not.

Some 30,000 people are estimated to have been killed during more than seven years of military rule in Argentina.