"NCIS" will never be the same again because Mark Harmon is finally leaving the show after 18 years of portraying the lead role of Leroy Jethro Gibbs.

His character was introduced in just a guest-starring role in two episodes of a legal TV drama series, "JAG," but in 2003, he starred in his show and became a fan favorite.

On Oct. 11, "NCIS" just aired the biggest episode of the show, and the frequent rumors about Harmon moving on to other projects finally happened.

Mark Harmon Leaving 'NCIS'

As many fans recall, the 18th season of "NCIS" was very tumultuous for Mark Harmon's character and himself in real life.

On the show, he faced suspension after attacking an animal abuser. Meanwhile, off-screen, he was reportedly considering leaving until he was informed that the show would go on without him.

Fans thought that Gibbs was leaving and that the show would come to an end after that season. But thankfully, Harmon went into contract negotiations, and by April 2021, CBS renewed the show for its 19th season. At the time, he was still on board.

But now it seems like his time is up, despite only showing up this season in a couple of seasons.

According to showrunner Steve Binder, Mark Harmon will not wholly leave because he is an executive producer on the show.

"So regarding the future of Gibbs, as long-time fans of the show may have noticed over the years... never count Leroy Jethro Gibbs out."

It was revealed that Mark Harmon's exit on the show was already expected since his on-screen duties were already scaled back a lot and the addition of a new agent on the show.

Gibbs already decided to say goodbye to his career following his suspension at the end of Season 18 for assaulting a murderer and dog abuser.

The Future of 'NCIS' Team Without Gibbs

In Leroy Jethro Gibbs' final episode, the killer's story was finished when Gibbs and McGee went to Alaska to see who hired him and why.

Though they succeeded and Gibbs was given his badge back, he realized that being in an unfamiliar place but at peace and knowing that he needed more of it, he decided to stay in Alaska.

Having the head of the squad continue living in peace only means that the NCIS team will know he's out there but will be shy to disturb him. But this won't stop him from making guest star appearances.

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Mark Harmon's Replacement on 'NCIS'

Gary Cole has just joined the cast of the hit series this season as a series regular, playing FBI Special Agent Alden Park.

According to TV Line's sources, his casting wasn't meant for a replacement for Harmon.

But it's obvious that the character will be an interesting one in his own right and wasn't even afraid to fight back against Gibbs just before he left.

However, it's nearly, if not, really impossible to replace Leroy Jethro Gibbs on the show because he had done an incredible job playing the beloved character for almost two decades.

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