"Oh, we'll miss her. I'm really aware, and we're all aware that audiences grow to love characters, and it's a big deal. And we honor that," Harmon said. "Fifteen years is a long time. People do what they do, and they move on and they do other things and that's part of life."
"It's given us, as a show, an opportunity to rebirth, to rejuvenate, to try new things, to grow," he added. "We adjust."
Harmon's TV Guide cover hits newsstands on Thursday, and NCIS airs Tuesdays on CBS.
See more on Perrette's exit in the video below.