"NCIS" fans, please sit down before reading this. Mark Harmon is bringing Gibbs to "NCIS: Origins" full-time.The "NCIS" prequel series centered on the iconic Leroy Jethro Gibbs (played as a youngster by Austin Stowell) has always featured executive producer Harmon, who provides the haunting, regretful voiceover.However, when "NCIS: Origins" Season 3 starts up on Tuesday nights in October, Harmon, 74, will appear in all episodes, the network confirmed on Tuesday, June 30. Gibbs will be part of a present-day mystery tied to his ‘90s Camp Pendleton days in a story that unfolds all season long.The official NCISVerse Instagram page celebrated the full-time Harmon return with a video showing two empty directors chairs near the set with "Gibbs" written on them in big letters."You'll see," Harmon says at the video's end, anticipating the question of how this will all work.Where is Mark Harmon on 'NCIS: Origins'?Harmon's Gibbs remains retired from NCIS work, living off the grid in Alaska since retiring in 2021. However, the silver-haired star appeared in the "NCIS: Origins" 2024 series premiere to kick it off.Older, wiser Gibbs made a special guest appearance during the first crossover event between "NCIS" and "NCIS: Origins" in November. In that episode, lone wolf Gibbs got a new special friend, an adorable dog. So he's not alone in Alaska."Origins" has never reached its full potential TV audience despite being a solid show in the "NCIS" universe. So why not bring back Harmon? The "NCIS" legend will draw and entice viewers to fall further for the young Gibbs training in Camp Pendleton in the early ‘90s, years prior to the events of "NCIS."It's all part of the "NCIS" canon, which is what makes it so fascinating."Origins" also stars Kyle Schmid, Mariel Molino, Tyla Abercrumbie, Diany Rodriguez and Caleb Foote. The series is show-run by David J. North, with Harmon's son Sean Harmon, who had played a younger version of Gibbs on "NCIS," as another executive producer.Sounds like there's going to be a lot of Gibbs in the house.How to watch 'NCIS: Origins'"NCIS: Origins" will air Tuesdays at 10 p.m. ET/PT this fall on CBS and can be streamed the following day on Paramount+.