A Hellfire missile fired by a CIA drone killed al-Qaeda leader Abu al-Khayr al-Masri late on Sunday while he was riding in a car near the northwestern Syrian city of Idlib, a U.S. intelligence official said on Wednesday.

The 59-year-old al-Masri, whose real name was Abdullah Muhammed Rajab Abdulrahman, was second-in-command to the group’s leader, Ayman al-Zawahiri, and a member of its shura council, said the official, who was briefed on the attack and spoke on condition of anonymity.

He also was married to one of Osama bin Laden’s daughters, the official added. CNN first reported the strike.

The official said Masri, as he was widely known, had sought refuge in Iran after the Sept. 11, 2001, attacks on the United States, and was believed to have been in Syria helping to direct Jabhat Fateh al-Sham, an al-Qaeda branch previously called the Nusra Front, the official said.

The Iranians released him from house arrest almost two years ago, in exchange for a diplomat being held hostage in Yemen by al-Qaeda in the Arabian Peninsula, the official said.

An Iranian diplomat held hostage in Yemen since 2013 returned home to Tehran in 2015 amid conflicting accounts of how he was freed from his unidentified abductors.

At the time Iran said the diplomat had been rescued by an Iranian intelligence operation in Yemen.

But Yemeni media run by the Iran-allied Houthi group said the diplomat was freed in a prisoner exchange that took place in another country.

Masri's death was the end of an almost 19-year U.S. hunt for him. A second U.S. official, also speaking on condition of anonymity, said Masri was thought to be one of the planners of the 1998 attacks on the U.S. embassies in Kenya and Tanzania.