(CNN) -- An FBI translator with a top-secret security clearance traveled to Syria in 2014 and married a key ISIS operative she had been assigned to investigate, CNN has learned.

The rogue employee, Daniela Greene, lied to the FBI about where she was going and warned her new husband he was under investigation, according to federal court records.

Greene's saga, which has never been publicized, exposes an embarrassing breach of national security at the FBI—an agency that has made its mission rooting out ISIS sympathizers across the country.

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