Mark Harmon appears clean-shaven in on-set photo reuniting with NCIS co-stars

Mark Harmon will always be Jethro Gibbs.

Though it has been five years since the former West Wing actor left NCIS, he has held close ties to the franchise via behind-the-scenes roles.

Most recently, he did return as his beloved character with a cameo on the Gibbs-centered prequel spin-off NCIS: Origins, which he also produces, and it appears he has taken a liking to reprising the role with some frequency.

Last week, NCIS fans enjoyed not one but two character revivals on NCIS: Origins, Mark as Jethro, as well as Emily Wickersham as Eleanor "Ellie" Bishop, who left the same year as Mark.

Following the multi-episode reunion, Emily took to Instagram and shared a series of heartwarming photos with Mark, starting with a selfie of the two hugging.

Among the other photos were behind-the-scenes, on set snaps with the rest of the cast, and more glimpses of a clean-shaven Mark looking eager to be back at work.

"A little bit of my origin story… I love this show, these people, and getting to be a tiny part of it," Emily wrote in her caption, and fans were quick to take to the comments section under the post and rave over it.

"This is very cool! I can't wait to see how you affect the story on Origins this season!" one wrote, as others followed suit with: "Love a Bishop pop in," and: "Little more than tiny part Em, you're a significant part of one of the most successful and enduring television shows in history. You should be proud of yourself!!" as well as: "Love what they are doing in Origins this Season… and getting to see Gibbs young and old is a big plus!!! So glad to see you in it too… miss you on NCIS."

Emily, speaking with TVInsider about the reunion and how it came about, shared: "I have been very close with [co-creator] David North for quite a long time since I worked on the OG NCIS, and I just got a call one day and we chatted about it and he kind of took my temperature on it. I mean, I've been such a fan of what he does in general, but what he's created over on Origins. So I was like, yeah, I'd love to be a part of it for a bit."

Gushing about reuniting with Mark, she said: "It was really fun. It was like we were just jumping back into it. It was as if no time had passed."

"Weve worked together for so many years and I think, I feel like we have such an easy back and forth. It was great. It was also kind of nostalgic for me. I haven't really worked with him in, I feel like it's been, I guess, six years now, which is crazy to me that that much time has gone by, but it really didn’t feel like that at all."

Emily's returning episode airs on CBS Tuesday, October 27.