NCIS' On-Set Vibe Post-Mark Harmon Is Much Different, According To Brian Dietzen – Exclusive

For 19 seasons, it can be argued that Mark Harmon carried "NCIS" on his back. His name certainly carried a lot of weight when the series first premiered, as he had previously starred on "St. Elsewhere" and "Chicago Hope." Playing Special Agent in Charge Leroy Jethro Gibbs, Harmon saw a lot of action on the show, which follows the highly-trained Washington, D.C.-based team of agents who investigate crimes connected to Navy and Marine Corps personnel.

Now in its 20th season, "NCIS" — which airs Mondays on CBS — has experienced a number of changes over the years, but the biggest so far is that Harmon decided to leave the show he helped build in 2021. His exit meant that there are just three original cast members dating back to Season 1, including Brian Dietzen as Dr. Jimmy Palmer, who exclusively spoke with Looper about what it has been like on the "NCIS" set since Harmon left.

While Gibbs' storyline remains open-ended after he decided to retire in Alaska on a whim, there are no plans for the 70-year-old Harmon to return to "NCIS."

"It's a massive change," admits Dietzen. "This whole television show has been built on the backs and the effort and the work of people like Mark Harmon, like Cote de Pablo, like Michael Weatherly, like Pauley Perrette. There's a lot of people that have made this thing the entity that it is, that have served their time, or however you want to put it. They've been family members, and Mark has certainly been the patriarch of this family for 19 solid years."

After Harmon exited the show, the vibe both on set and off shifted immediately. "You feel that loss right away on an energy level, but also on a personal level day to day — and on a story level as well, because everything must shift as the entire 'NCIS' cast is no longer orbiting around this one central figure anymore," says Dietzen. "Those stories have to become much more ensemble than they ever have been before, which is what our show experienced last year."

On a more personal note, Dietzen reflects on his time working with Harmon and what it's been like to lose so many high-profile cast members over the years.

"I'm really thankful I got to work with Mark and call him a friend for that many years," he says. "I feel similarly about everybody I've worked with there. It's been a wonderful, wonderful place for 20 years. As people come into our set and people go, it feels like you're making new family members and you're making new friends all the time."

Season 20 of "NCIS" airs Mondays on CBS at 9 p.m. ET/PT and is available to stream live and on demand on Paramount+.