The longtime chief of the Basque separatist militant group ETA, which is designated as a “terrorist” by the U.S., was arrested Thursday in the French Alps after more than 17 years on the run.

Josu Ternerna – whose real name is Jose Antonio Urrutikoetxea Bengoetxea – was nabbed in a joint French-Spanish police operation in Sallanches, a town of 16,000 in eastern France’s Alps region near mountain and ski resorts.

Police said Ternera was arrested after he fell seriously ill and Spanish police were tipped off by French authorities that he was on his way to the hospital, the BBC reported, citing local reports.

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The 69-year-old has been the most wanted ETA member since 2002. Interpol, the global police coordination body, had issued a red alert against him and Spanish authorities accuse him of crimes against humanity.

ETA, whose initials stand for “Euskadi ta Askatasuma” or “Basque Homeland and Freedom” in the Basque language, has been accused of killing more than 850 people during its violent campaign to create an independent state in northern Spain and southern France.

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Investigators tracked Ternera’s links to ETA since its violence activities shot the group to international prominence in the 1970s. He was one of the negotiators who sat down with Spanish government envoys for talks to try to end the group’s activists in the mid-2000s.

He went on to become a lawmaker in the Basque regional parliament but went into hiding in late 2002 after Spain’s Supreme Court summoned him for his alleged involvement in a bomb attack in the barracks of the Civil Guard in Zaragoza that killed 11 people, including six minors, in December 1987.

In homage to those victims, investigators dubbed the mission to arrest Ternera “Operation Stolen Childhood.”

According to the BBC, Ternera will likely be imprisoned in France after a French court last June sentenced him to eight years for leading a “terrorist” group. However, Spain is likely to request his extradition over the Zaragoza attack and his alleged involvement in other crimes, including the murder of a Michelin manager in 1980.

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ETA announced in May 2018 that it would be disbanding. Ternera is believed to have been one of the two ETA members who read a statement announcing the dismantling in an audio recording released last May.

In the audio clip, he said that ETA had “completely dismantled all of its structures” and would “no longer express political positions, promote initiatives or interact with other actors.” He said former members would “continue the struggle for a reunited, independent, socialist Basque-speaking and non-patriarchal Basque country.”

Spanish authorities said Ternera was living near Saint-Gervais-Les-Bains, an Alpine village frequented by winter sports aficionados near Mont Blanc.

The Associated Press contributed to this report.