Al Qaeda's next leader will likely be more brutal than his predecessors to attract a younger generation of terrorists, an Army special operations veteran and drone expert told Fox News.

A CIA drone strike in Afghanistan over the weekend killed Ayman al-Zawahri, the al Qaeda leader who succeeded Usama bin Laden. He was a key figure in planning the 9/11 terror attacks.

"I think if anyone replaces him, they'll be a bit more aggressive in their operations, sort of try and gather a bit more credibility with the younger generation of terrorists that exist," said Brett Velicovich, who wrote the book "Drone Warrior: An Elite Soldier's Inside Account of the Hunt for America's Most Dangerous Enemies." 

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Al Qaeda leader Ayman Al Zawahri speaks on bin Laden's death

Al Qaeda leader Ayman al-Zawahri speaks on the 11th anniversary of Usama bin Laden's death. (AP Photo/Mazhar Ali Khan, File)

The younger, more militant generation consider al Qaeda "their father or grandfather's terrorist group" in comparison to more brutal groups like ISIS, Velicovich told Fox News, noting that Zawahri's successor could adopt more violent tactics to compete with these newer terror groups for recruits. 

The CIA secretly intensified its search of Zawahiri after the Taliban took control of Afghanistan, a person briefed on the effort told The New York Times, noting that the al Qaeda leader spent years avoiding the country.

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"Zawahri was always the one that got away," Velicovich said. "His death is going to reverberate across al Qaeda, and it's going to show them they can't just operate with impunity around the world."

The Taliban condemned the attack in a statement and said it hit a residential house. The group tweeted that the strike violated the terms of the Doha agreement, the arrangement that set terms leading to America withdrawing its troops from Afghanistan.

Al Qaeda leader Ayman Al Zawahri's FBI photo

Al Qaeda leader Ayman al-Zawahri's FBI "Most Wanted" mugshot (Federal Bureau of Investigations)

But Velicovich said Zawahri's presence in Kabul indicates that the Taliban allowed him to operate there, which violates the Doha agreement. 

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"They're clearly still working together, despite what they've been saying," Velicovich said. 

He added that this strike sends a strong message to terrorist leaders who think they can continue to operate in Afghanistan unchecked. 

Al Qaeda leader Ayman Al Zawahri speaks in a filmed address

This image taken from a video issued by al-Sahab, al Qaeda's media branch, shows al Qaeda leader Ayman al-Zawahri speaking. (As-Sahab via AP)

"Now justice has been delivered and this terrorist leader is no more," President Biden said in an address from the White House on Monday night. "No matter how long it takes, no matter where you hide if you are a threat to our people, the United States will find you and take you out."

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Biden, when defending his decision to withdrawal from Afghanistan, said in August 201 that al Qaeda was "gone." But Gen. Mark Milley, the chairman of the Joint Chiefs of Staff, said the following month that terror groups could grow faster without the presence of American troops.

 Velicovich told Fox News the CIA strike was a "very good thing" and said it proves the U.S. is still able to fight the War on Terror without a presence in the region.

"No matter where the U.S. is, no matter where terrorism currently is located, the U.S. is going to continue to chase down the enemies, no matter what," he said.