NCIS Producer and star Mark Harmon knew he had found his young Leroy Jethro Gibbs the first time he saw him.

When Bridge of Spies Star Austin Stowell came to audition for the prequel series NCIS: OriginsHarmon recalled that he “felt the room twitching a little bit” even before he said anything. Harmon recently told us PEOPLE about finding the younger version of the character he played for 19 seasons on the flagship series. “There was a lot of competition there,” Harmon remembers. “There were a lot of good people. I would say there were really few that got the attention that Austin did.”

Harmon even recalled that Stowell “walked out and someone said, 'I'll just say it, that's a movie star.'”

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Harmon played Leroy Jethro Gibbs, a former Marine Corps sniper turned special agent and team commander for the Naval Criminal Investigative Service (NCIS) from 2003 to 2021. The long-running CBS procedural has already spawned several spin-offs with varying degrees of success over the years, starting NCIS: New Orleanswhich Harmon co-produced NCIS: Los Angeles, NCIS: Sydneyand the recently canceled NCIS: Hawaii.

A spin-off about the events that led Gibbs to his position at NCIS was announced in January, with Harmon on board as co-producer. After extensive speculation as to who would play the young Gibbs (with the exception of Sean Harmon, the actor's son, who previously played a younger version of Gibbs). NCIS but returned Origins (serving solely as an executive producer), Stowell was announced as the official choice in March.

Of the kismet of Stowell's casting, Harmon noted, “I can say that about every role that was cast on this show because they all came one after the other. We got everyone we wanted.” In addition to the Gibbs character NCIS: Origins takes on the character of Mike Franks, the head of the Major Case Response Team and mentor to Gibbs.

Muse Watson played the older Franks in the flagship series, while Kyle Schmid (to be human, Big sky) was cast as Origins' younger counterpart.

In conversation with Weekly entertainment in September, NCIS Writer and executive producer David J. North said: Origins The team “just knew when Austin came in that he was Gibbs… He embodied it. His talent is limitless – his dedication to the role, his study of Mark, the study of the show – he has a leadership quality similar to Mark's on set that bleeds into the character of Gibbs.

“'You always have all of me,'” the actor recalled telling North and co-writer and executive producer Gina Lucita Monreal. “I just want to give everything for it. I know what it means to the fans. I know what Gibbs means to a lot of people out there. I know what the show means to a lot of people out there, and I don't want to let them down.

As an added vote of confidence in the new series, Harmon herself will step back into the spotlight behind the camera in tonight's series premiere. Harmon will occasionally appear as the older Gibbs, recounting the past experiences that led him to work with NCIS that continue into the future Origins.

NCIS: Origins Premieres Monday, October 14th at 9pm ET/PT on CBS and streaming on Paramount+.