FBI Executive Assistant Director Carl Ghattas has called it quits.

Ghattas, who heads the Bureau’s National Security Branch, is also described as the most experienced counterterrorism agent on the FBI’s rolls. He “leads the FBI’s operations and intelligence efforts involving all national security matters, ranging from terrorism to espionage to weapons of mass destruction,” according to the FBI.

Ghattas decided to retire Thursday, the fourth top FBI agent to walk away in the last week. But Ghattas’ departure is certainly the biggest. By far.

Ghtattas, a shrewd operator inside the FBI who managed to keep his name away from negative news stories, is best friends with fired FBI Deputy Director Andrew McCabe. Both reportedly attended Duke University during undergrad and went on to law school. McCabe and Ghattas reportedly roomed together at Duke, where McCabe also met his wife, Dr. Jill McCabe.

McCabe often sported a flashy Porsche, zipping in and out of the FBI parking garage under headquarters off Pennsylvania Ave in D.C. Then Ghattas also did the same, purchasing his own Porsche reportedly and driving it to work. Many agents fumed at the optics of the FBI’s top brass cruising around the beltway in Porches, but that didn’t seem to stop the duo and then-Director James Comey was oblivious to the optics — a pattern all now see during Comey’s tenure.

McCabe often described Ghattas as his personal legal advisor and wherever McCabe was and was doing, you could expect Ghattas wasn’t far behind, several FBI sources said.

“Ghattas was McCabe’s wing man,” one FBI agent said. “He was a better operator than McCabe but you did not want to cross either one of them because there was a mean streak there for sure and it just wan’t worth it on any level.”

But without McCabe’s protection, lost when he was fired, Ghattas wasn’t the same politically powerful agent, sources said. Couple that with emerging news that the House Intelligence Committee investigators said Ghattas’ name has surfaced in a matter they are investigating, and “the writing was one the wall for Ghattas” to exit the FBI as one agent put it.

Before McCabe’s firing, Ghattas was jockeying to become the FBI’s SES liaison with the Central Intelligence Agency, National Security Agency and White House but never did get the post, which would have been considered a large step down for Ghattas. FBI sources said.