Much of the basis around Mark's NCIS departure seemed to stem from his plans to retire. Fans theorized that he left the show to concentrate on moving to the family's Montana ranch for a life out of the limelight.

This would certainly line up with their desire to keep their professional lives separate from their personal lives.

"It's not even a choice. It's who we are," Mark said in an interview with TV Insider in 2017 about his and his wife's life of privacy. "We stay home. A lot. I'm not a Twitter guy or a Facebook. Our sons aren't into that either. Pam and I have both made a living in this business, and still, there's a part of that that's just not natural."

Finding a replacement for a character like Gibbs or an actor like Mark Harmon won't be easy, especially after almost the entire Harmon family left their mark on NCIS.