NCIS legend Mark Harmon is officially returning to the small screen in CBS's highly-anticipated spin-off, NCIS: Origins. Fans will be treated to a surprise appearance from Leroy Jethro Gibbs in the very first episode.

Austin Stowell will take over as a young Leroy Jethro Gibbs in NCIS: Origins, but not before the baton is officially passed. Here's what we know.

Mark Harmon, who played the 'NCIS' lead Leroy Jethro Gibbs for 18 years, is returning for an appearance on ‘NCIS: Origins’

According to TVLine and Deadline, NCIS: Origins co-showrunner David J. North revealed during a panel discussion with reporters on Thursday, Sept. 19, that Harmon would briefly appear on the show's Monday, Oct. 14 premiere, in addition to narrating the series and being one of its executive producers.

It’s not supposed to be about old Leroy Gibbs — this is about his younger self coming up in the Naval Criminal Investigative Service — but Mark Harmon will appear briefly in the premiere episode of NCIS: Origins.

Mark Harmon once shared what it might take for him to return to the ‘NCIS’ franchise after his very peaceful exit.

While North didn't confirm how Harmon will show up in the episode, he did leave the door open for more possible appearances in future episodes. "We are focusing on him telling the

Mark Harmon is set to make his first onscreen appearance as NCIS fan-favorite character Leroy Jethro Gibbs in three years.