The 70-year-old actor said goodbye to the procedural in the fourth episode of season 19 when his character Special Agent Leroy Jethro Gibbs decided to stay in Alaska indefinitely after solving a case.
"What has always drawn me here is the character I play and to keep it fresh and to keep it challenging," Harmon said in a special featurette on the show's season 19 DVD release, per Entertainment Tonight. "Plot-wise, this character has taken the path that it did. I thought it was honest and OK with."
Harmon — who starred on the series since its premiere in 2003 — also shared that he believed that his beloved character is "not retired," adding, "The character is living in Alaska as far as I know."
In Harmon's final NCIS episode, his character said he did not plan to return home from Alaska.
"I'm not going back, Tim," he told Special Agent Timothy McGee (Sean Murray) while fishing. "I'm not going back home."
Monty Brinton/CBS via Getty
Gibbs then tells McGee that he "could not have hoped for anyone better" to work with over the past 18 years before the partners hugged, closing out the scene.
Following the episode, executive producer Steve Binder opened up about Harmon's exit for the long-running series.
"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," he told PEOPLE in a statement. "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."
"Mark's always been part of the show, Mark's always going to be part of the show," CBS Entertainment President Kelly Kahl told Deadline in September 2021. "In terms of his on-air appearances, we're just going to have to see how it plays out going forward."
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NCIS: The Nineteenth Season is out on DVD on Tuesday. NCIS will return to CBS for its 20th season on Sept. 19.