Mark Harmon Exits NCIS After 18-Plus Seasons -- See How Gibbs Says Goodbye

Fans have been anticipating it all season long, but that didn't make it any easier when it became clear that Monday's episode of "NCIS" would be Mark Harmon's last.

Harmon originated the character of Gibbs in a guest role on "JAG" before spinning off into "NCIS," now in its 19th season. After narrowly surviving a boat explosion in the Season 18 finale, Gibbs made a quieter bow in the fourth episode of this season.

After he and Special Agent McGee (Sean Murray) tracked a hitman to Alaska, Gibbs made the decision that this was his moment, and this was the place.

While fishing in the Alaskan wilderness, Gibbs told McGee, "I'm not going back home."

When McGee asked him what he was hoping to find in Alaska, Gibbs responded, "I don't know. My gut's telling me I'll know when I find it." But it may be that he'd already found it, after so many years taking down bad guys.

He shared with McGee that what he really felt in Alaska was peace, and he's "not ready to let it go." While Harmon exits the series as its lead, he remains an executive producer. And with an exit near the water, rather than trying to survive on it, the door is wide open for a return appearance, should the interest arise.

"As an executive producer and dear friend, Mark continues to be an integral part of the fabric of the show," said showrunner Steve Binder in a statement tied to Harmon's last appearance, per Deadline.

"Our north star has always been staying true to our characters, and that truth has always guided the stories we tell and where those characters go. 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."

That leaves "NCIS" in a rare place in television history, a top-rated show looking ahead to a future without its star. Some of those shows have managed to continue their winning streaks under new on-screen leadership.

For "NCIS," that leadership has been slowly growing, with the addition of Gary Cole as Special Agent Park and a strong and well-established ensemble cast. Still, it's always hard to lose the face of a franchise.

Fans took to Twitter to pay tribute to Harmon, getting Gibbs trending, after nearly two decades together: