A legendary run has come to an end.

On Monday night, following 18-plus seasons as the lead of television's most-watched drama, Mark Harmon said goodbye.

This sentence feels almost incomprehensible to write, yet it's true:

Leroy Jethro Gibbs has left NCIS.

We were told way back in April that the beloved series would be coming back for Season 19 -- despite the questionable status of its long-running lead star.

Then, in June, it was confirmed by reliable network sources that Harmon would only appear in a handful of NCIS episodes this fall.

As it turns out, this number of NCIS episodes turned out to be four, as the show wrote Gibbs off on an installment titled "Great Wide Open."

Consider this a major SPOILER ALERT if you have not yet seen the way in which Harmon departed the show that made him uber rich and famous, and then scroll down to find out...

The dramatic episode centered on Gibbs and Special Agent Timothy McGee (Sean Murray) out in Alaska, attempting to solve the case of a contract killer hired by a local company.

In speaking with the father of a reporter murdered by this suspect, Gibbs indicated at one point that he, too, has suffered the loss of a child.

“How do you get through the days?” asked the dad.

Gibbs bowed his head and admitted: “Some days I don’t.”

Shortly afterward, we cut to one of several farewell scenes presented as flashbacks... with Vance meeting up with Gibbs at the diner to deliver a small shopping bag containing a satellite phone, to use when in Alaska.

Gibbs then managed to choke out a goodbye to his close friend and colleague, eventually dunking of his old clamshell phone in his coffee on the table.

“It had a good run,” he noted.

In a second flashback, Ducky stopped by Gibbs’ house just as he was about to get a ride to the airport.

"There’s nothing to worry about, Duck," Gibbs assured his pal after Ducky expresses concern about losing team members.

Gibbs then confessed that he's been “searching,” although he wasn't certain for what. Be

Prior to fore heading off to Alaska, Gibbs gave Ducky a big hug and said: “You are a great friend. I appreciate you more than you know.”

Finally, in the aftermath of the case getting solved, Gibbs took McGee fly fishing in Alaska and opened up like never before about his own father and childhood.

It also talked about fishing... but not really, of course.

“You have to find your rhythm; not mine…. Be patient. It’s about progress, not perfection,” he told the senior agent to whom he was about to turn over the keys to the proverbial car.

“Once you know the basics, the rest comes from inside.”

And when Gibbs didn't get on the plane to head home?

“I’m not going back, Tim…. I’m not going back home,” he stated, explaining that “this sense of peace, I have not had this since Shannon and Kelly died. And I am not ready to let it go...

“I could not have hoped for anyone better to watch my back for the past 18 years than you, Tim."

The episode wrapped up with Gibbs pulling his number-two into the biggest of bear hugs, saying:

“I love you” -- and McGee, in response, then said, through tears, “I love you, too,” before boarding the sea plane and leaving Gibbs behind.

Alone.

And at peace.

In a statement tied to the episode’s airing, NCIS showrunner Steve Binder praised Harmon, who had headlined the series since its launch 18 years ago... while also teasing a possible return down the line:

“As an executive producer and dear friend, Mark continues to be an integral part of the fabric of the show.

"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.”