Sean, who serves as an executive producer on the prequel series, will appear in the second episode of season 3
NEED TO KNOW
- Mark Harmon’s son, Sean Harmon, will guest star in NCIS: Origins
- Sean, who serves as an executive producer on the prequel series, previously played the younger version of his father’s Special Agent Leroy Jethro Gibbs on the mainline NCIS series
- Mark will appear in every episode of Origins‘ third season
Mark Harmon’s son, Sean Harmon, is returning to act in the NCIS universe.
Three months after CBS announced that Mark, 75, would be returning as Leroy Jethro Gibbs in all episodes of NCIS: Origins’ third season, the network also announced that Sean, 38, will appear in an upcoming episode of the prequel series.
The second episode of the season, “My Own Worst Enemy,” arrives on Oct. 13 and features Sean as FBI agent Casey Bloom, per a release from Paramount. It’s unclear if the father-son duo will have scenes together.
Credit: Steve Granitz/FilmMagic
According to a synopsis, the episode follows Gibbs (Mark) as he “returns to civilization and calls in a favor from old friend Woody (Bobby Moynihan),” while the 1992 timeline has the team helping Woody “when he’s accused of murdering a bowling rival.” The episode is written by Laura Valdivia and directed by Jessica Lowrey.
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Sean, who serves as an executive producer alongside his dad on Origins, has previously played a younger version of his father’s character on the mainline NCIS. Notably, Austin Stowell stars as the younger Gibbs in Origins, with Mark having provided narration for the series since its debut in October 2024.
In 2024, Mark told Variety why his son was no longer acting as the younger Gibbs. “He’s an actor, writer, producer, a surfer, he does a lot of things. You have to come to decisions about what you want to do in life, or what you think’s important. I just think he made a choice and had to make a decision in some ways,” he said. “He likes executive producing.”
Per CBS, the elder Harmon makes his on-screen return in the new season for a “present-day mystery tied to his ‘90s Camp Pendleton days in an action-packed story that unfolds all season long.” While he appeared during its 2024 premiere and again during a November 2025 NCIS crossover event, his latest return will be for much longer.
Mark first played Gibbs for 18 seasons on NCIS before departing in 2021. His most recent appearance as the character came in the November episode “Funny How Time Slips Away,” as he told The Wrap it was “interesting to be able to reveal a glimpse of how he is living.”
“It’s a very short little bit, but the audience will get a chance to know things about him that they don’t know already,” he said.
The third season of NCIS: Origins will air Tuesdays at 10 p.m. ET on CBS, directly after NCIS: New York at 9 p.m. ET and NCIS at 8 p.m. NCIS: Origins’ new episodes will also be available to stream on Paramount+. It arrives on Oct. 6.
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