The prequel will tell the story of how Leroy Jethro Gibbs became an NCIS agent in 1991.
Mark and Sean Harmon are ready to peel back and reveal everything there is to know about Leroy Jethro Gibbs.
The father-son duo are serving as executive producers of NCIS: Origins, the prequel to the iconic NCIS franchise set to come to the CBS fall lineup later this year. And while speaking to ET's Kevin Frazier on Thursday at the CBS Schedule Reveal Celebration at the Paramount Studios Lot in Los Angeles, California, the Harmons made it clear that they are laser-focused on how exactly they want to travel down memory lane.
"It's all going to be a time that we haven't traveled before. It's 1990, so it's something we're all looking forward to," said Mark, who portrayed Special Agent Gibbs during his incredible 19-season run on NCIS. "It will be different."
NCIS: Origins is the brainchild of Sean, who concocted the idea while playing the younger version of Special Agent Gibbs during flashback episodes.
"This is an idea we worked on for a long time and just really happy to finally be at this point in the process," Sean said. "I like to think he [Mark] made me the man I am today. None of this is possible without this character. NCIS has been a huge part of my life as well ... just getting a chance to tell this story that we're telling here is pretty special."
The prequel will star Austin Stowell as Special Agent Gibbs, and the series will chronicle his start at the famed law enforcement agency. The series will also star Mariel Molino as Special Agent Lala Dominguez, Kyle Schmid as the formidable Mike Franks, and Tyla Abercrombie as Field Operations Support Officer Mary Jo Sullivan. The prequel includes recurring roles for Robert Taylor as Jackson Gibbs (Special Agent Gibbs' father), Daniel Bellomy as Special Agent Granville "Granny" Dawson and Caleb Foote as Special Agent Benjamin "Randy" Randolf.
The series, which will film on the Paramount lot, will also offer a bit of an Easter egg hunt for devout fans of the iconic franchise.
"I think it's part of what [producers] Gina [Lucita Monreal] and David [North] have planned, and they'd be the ones that tell you that," Mark shared. "But it's the 1990s. It's a different time. The show's going to be different. The cast we got is different and it feels good at this moment, but we still have a lot of work to do. So we'll see when it comes out and you'll be the first one to say whether it works or doesn't."
Mark returns to the franchise -- as an executive producer and narrator to the series -- for the first since leaving the iconic franchise in 2022 after 19 seasons. He spoke to ET back in November and shared that he didn't expect to like NCIS.
"I didn't expect to like the script as much as I did when I first read it," Mark said. "I was reading other things and I was also trying to stay home -- young family and I wanted to try and be home more."
But he liked the character's name. And he was in.
"I read 'Leroy Jethro Gibbs' and thought, 'Huh, I like that name,'" Mark said of what initially piqued his interest. "And then for a brief second when I decided that I liked the idea of the project, the name changed."
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