NCIS: Origins Brings Mark Harmon’s Son Back to the Franchise — But Sean Harmon Won’t Be Playing Young Gibbs This Time

NCIS: Origins is bringing back an actor with a particularly unusual connection to Leroy Jethro Gibbs — but this time, he’ll be playing someone completely different.

Sean Harmon, the son of longtime NCIS star Mark Harmon, previously portrayed a younger version of his father’s iconic character in eight episodes of the original series.

When NCIS: Origins launched, however, Austin Stowell took over the role of Gibbs for the prequel’s 1990s storyline.

Now Sean is finally stepping in front of the camera on Origins — not as Gibbs, but as a brand-new character.

And his appearance comes during a season that is also giving Mark Harmon a much larger onscreen role.

Sean Harmon returns to the NCIS universe

CBS has revealed details for Season 3 Episode 2, titled “My Own Worst Enemy,” which will air on October 13.

The episode will introduce Sean Harmon as FBI Agent Casey Bloom.

Sean already works behind the scenes on NCIS: Origins as an executive producer, making the guest appearance an unexpected return to acting within the franchise.

Longtime viewers may remember him from the original NCIS, where he appeared in flashbacks as young Gibbs.

His appearances included scenes opposite Adam Campbell, who played the younger version of Donald “Ducky” Mallard, the beloved character portrayed in the present-day timeline by the late David McCallum.

But Origins gave Gibbs’ younger years a fresh start.

Why Sean Harmon didn’t continue playing young Gibbs

When the prequel arrived two years ago, Austin Stowell was selected to portray Gibbs in the show’s 1990s timeline.

Mark Harmon previously explained that his son’s absence from the starring role wasn’t simply about replacing one actor with another.

Speaking ahead of the show’s 2024 premiere, Mark described Sean as someone with several different interests.

“He’s an actor, writer, producer, a surfer, he does a lot of things,” he said.

According to Mark, Sean had reached a point where he needed to decide which areas he wanted to prioritise.

“He likes executive producing,” Mark added.

That role has kept Sean connected to the Gibbs story behind the camera.

Season 3 will now bring him back in front of it.

One episode will unfold across two timelines

“My Own Worst Enemy” will connect the present-day Gibbs storyline with a mystery unfolding in 1992.

In the present, Mark Harmon’s Gibbs returns to civilization and contacts his old friend Woody, played by Bobby Moynihan, because he needs a favor.

Meanwhile, the 1992 storyline finds the younger team facing a very different problem.

Woody has been accused of murdering a bowling rival, forcing the team to come together to help him.

It is within this episode that Sean Harmon will appear as FBI Agent Casey Bloom.

Exactly how Bloom fits into the case has not yet been revealed.

Mark Harmon is also returning in a much bigger way

Sean isn’t the only Harmon getting more screen time.

Although Mark Harmon has narrated NCIS: Origins from the beginning and serves as an executive producer, Season 3 significantly expands his physical presence in the series.

He is set to appear onscreen in every episode of the new season.

The Season 3 trailer places present-day Gibbs in Alaska, where Woody comes to see him.

“I came to Alaska to find peace, but ghosts from my past found me,” Gibbs says in voiceover.

He adds: “I know now peace never lasts.”

Gibbs is also shown telling Woody that he needs him to do a favor.

The storyline creates another bridge between the character’s past and present, allowing the prequel to explore how events from decades earlier continue to affect the older Gibbs.

A rare father-and-son NCIS connection

Sean Harmon’s casting creates an unusual piece of NCIS history.

He first entered the franchise by literally playing a younger version of his father’s character.

Austin Stowell now owns that role in Origins, while Sean has moved behind the camera as an executive producer.

Season 3 completes another turn in that journey by bringing him back as an entirely separate character.

For longtime fans, that means the actor they once knew as young Gibbs will soon be standing inside the same universe without playing Gibbs at all.

And with Mark Harmon appearing throughout the season, both father and son will once again be part of the NCIS story — just in very different ways.

NCIS: Origins Season 3 premieres Tuesday, October 6 on CBS, with Sean Harmon’s episode airing October 13.