David McCallum's “NCIS” Costars, Ex Joan Collins and Honor Late Actor: 'He Made Every Moment Count'

“All of us on were honored to have toed a mark opposite him,” Mark Harmon wrote of his former costar on the long-running CBS procedural

David McCallum’s friends and NCIS family are remembering the late actor.

McCallum’s fellow costars on the CBS hit, including Mark Harmon and Michael Weatherly, as well as his friends and colleagues over the years paid tribute to the NCIS and The Man from U.N.C.L.E. star after his death on Monday at the age of 90.

Related: 'NCIS' Star David McCallum Dead at 90: 'A Scholar and a Gentleman'

Harmon, who played NCIS lead Leroy Gibbs alongside McCallum’s Donald “Ducky” Mallard for 19 seasons, wrote in a statement shared with Deadline that he was “in awe” of the longtime actor “when I first met him.”

Harmon noted that McCallum “lived a great, full, long life” and also shared, “All of us on the show were honored to have toed a mark opposite him.”

Weatherly posted a tribute on X (formerly known as Twitter), writing that McCallum “made every moment count, in life and on set,” alongside what appeared to be an autographed photo from the actor addressed to him.

“Let’s raise a jug and celebrate a funny fantastic authentic man. I’ve only got 3 autographs,” Weatherly added. “[Sean] Connery, Tony Bennett and McCallum. I felt the same way as Steve McQueen in this picture from The Great Escape: Wow! It’s David McCallum!”

“No one did it better,” he summed up. “We were lucky to have him bring us Ducky. Let’s send all the love in the world to his beautiful family. Rest In Peace David.”

Pauley Perrette, who starred as NCIS chief forensic scientist Abby Sciutto for 15 seasons, shared several photos on Instagram of her and McCallum posing together over the years, noting: “What a life. What a legend. What a journey.”

“And your legacy will always be the love you have for your family,” she wrote. “Love to [his wife] Katherine and the kids and the grandkids, your absolutely very favorite things.”

Emily Wickersham, who said she “had the pleasure of working” with McCallum “for many years” on NCIS, called the star “an utmost professional and a true legend” on her Instagram Story. “I will miss you David,” she added.

NCIS alum Katrina Law also shared a photo of the actor dressed up as Ducky alongside the caption "R.I.P."

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Brian Dietzen, who plays the protégé of McCallum’s character Ducky, put up a lengthy tribute on Instagram that called McCallum a “mentor,” a “great scene partner” and a “dear friend.”

“He was a joy to work with,” Dietzen wrote. “Always had a smile. Always had something new to add to the page, and ALWAYS had the ability to steal every scene he was in! He had a quick and wry sense of humor and was generous with advice when I asked for it.”

He added, “The friendship and respect people saw between Ducky and Jimmy over the years mirrored the relationship we’d developed off camera. Whether it was going on field trips for character research, attending charity events or catching some golf together, he was always up for an adventure.”

Beyond McCallum’s NCIS family, several of the late actor’s friends including Joan Collins shared a heartfelt post commemorating her drama school paramour and The Man from U.N.C.L.E. costar.

“So sad that #davidmccallum - my first boyfriend at #rada - has died,” the Dynasty star wrote on Instagram alongside an old photo of the two on set. “A fine #actor a great #talent and a true #gentleman. Loved working with him on #manfromuncle #rip #ripdavidmccallum.”

Robert Wagner, who previously starred with McCallum on Escape from Colditz and other films, shared a photo on Instagram of the two standing side by side in a black-and-white film.

“The world lost a great talent today,” he captioned the post. “David was a brilliant actor who I had the pleasure of working with on several different projects. Thoughts to his wife, Katherine and to his sons and daughter.”

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CBS announced on Monday that McCallum died “peacefully” of natural causes surrounded by family at New York Presbyterian Hospital.

The actor is survived by his wife of 56 years, Katherine McCallum, his sons Paul, Valentine and Peter McCallum, his daughter Sophie McCallum and his eight grandchildren.

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