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Actor Mark Harmon played Leroy Jethro Gibbs on NCIS for 19 seasons.
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The former CBS star became a first-time grandfather earlier in 2025.
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Mark’s daughter-in-law Courtney Prather revealed she and husband Sean Harmon welcomed son Cooper Knox on May 22.
Mark Harmon just added a heartfelt new title to the long list of roles he’s held throughout his life.
Over the years of being in the world of Hollywood, people mainly know him for portraying Leroy Jethro Gibbs on NCIS. But fans of the hit CBS drama seemingly missed the news of him taking on a brand-new role in his life, as his daughter-in-law Courtney Prather (who’s married to Mark’s son Sean Harmon, whom Mark shares with wife Pam Dawber) dropped an emotional family update.
Sharing a personal announcement on Instagram on July 4, Courtney revealed she and Sean welcomed their first child Cooper Knox back in May. And if that wasn’t enough, Courtney also gave a rare look at what life has been like with the couple’s son.
“1 month with you 💙,” she wrote in the caption at the time. “Cooper Knox Harmon ~ 5.22.25.”
As soon as fans learned that Mark had quietly become a first-time grandfather, they immediately ran to Courtney’s Instagram to celebrate the news.
As some may remember, Sean has been pretty integrated into his dad’s world when it comes to NCIS. He not only portrayed a younger Gibbs several times on the original series, he and Mark are both executive producers for the NCIS: Origins spinoff that premiered in October 2024.
As for Sean’s personal life, he and Courtney got engaged back in August 2021 after five years of being together. The couple tied the knot just over a year later in November 2022, with Cooper’s birth being the next stage in their lives.
Even though Mark hasn’t publicly commented on becoming a grandfather, we are sending the Harmon family much love in this new chapter!
“He is absolutely adorable 😍 congratulations mama and daddy 💙,” one person wrote in the comments. “So very happy for you! Such a sweet family and handsome baby boy. ❤️,” another declared. “We need a photo of Cooper and grampa Mark,” a different follower noted.
