Brian Dietzen, star of NCIS, remembers his “meaningful” final conversation with David McCallum and creating the show’s “celebration” tribute (exclusive)

Dietzen tells PEOPLE that he and co-writer Scott Williams aimed to honour the late actor’s memory “by telling a good story” and “do justice in honouring a TV legend.”

Brian Dietzen, David McCallum’s costar from NCIS, was able to say a heartfelt farewell to his friend before his death in September of last year.

Dietzen, 46, discusses his final chat with the late actor in an exclusive interview with PEOPLE before to Monday night’s NCIS homage to McCallum. The actor passed away a few days earlier.

“I’ll say that I got to speak to him on his birthday, which was wonderful,” he continues. That Tuesday was the event. He was in the hospital already, obviously not doing well, and he passed away that weekend.”

Dietzen describes how Katherine, McCallum’s wife, handed him the phone while he was in the hospital. He continues, saying Dietzen was “very happy to hear it” and that The Great Escape star was “very coherent.”

“He was, obviously, going through some health issues and whatnot, but he had this stretch of time in that last week where he got to chat with all of his family, his kids, and obviously, Katherine,” he says. “And I was lucky enough that when I called in, I got to actually talk to him.”

“I’m so glad that I got to speak to him one last time and I got to tell him how I felt,” Dietzen continues, even if he intends to keep the “contents of the call” between them. That was therefore extremely significant.”

At New York Presbyterian Hospital in September 2023, McCallum passed away “peacefully” from natural causes in the company of friends, according to a statement made at the time by CBS.

The Scottish actor immigrated to the United States in 1961 after completing his studies at the Royal Academy of Dramatic Arts and working for a number of years in repertory theatre in the United Kingdom.

He was cast opposite Robert Vaughn as Illya Kuryakin in The Man from U.N.C.L.E. For the part, he received two Emmys and a Golden nomination. McCallum first gained notoriety for his role as Dr. Donald “Ducky” Mallard on the police drama NCIS in 2003.