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Boston Blue‘s major casting shake-up has fans divided.

In July 2025, PEOPLE confirmed that Andrew Terraciano would not be returning to play Sean Reagan, the son of Danny Reagan (Donnie Wahlberg), in CBS’ new series Boston Blue — a spinoff of Blue Bloods.

The decision came as a shock to many viewers, considering Terraciano played Sean on Blue Bloods for 14 seasons from 2010 to 2024 alongside Wahlberg. Ahead of the premiere of Boston Blue on Oct. 17, 2025, co-showrunner Brandon Margolis spoke to TVLine about bringing actor Mika Amonsen on board as Sean.

“First of all, we love Andrew’s work from the original series and loved watching him grow up on TV,” he said. “But once we realized we were telling a very new chapter in this character’s life, creatively it made sense to find an actor with a different energy.”

Here’s everything to know about why Boston Blue recast Donnie Wahlberg’s on-screen son.

Why did Boston Blue recast Donnie Wahlberg’s on-screen son?

Co-showrunner Margolis told Variety in October 2025 that the decision to recast Amonsen as Danny was made solely for creative reasons.

Boston Blue introduces major changes for the Reagan family. In the spinoff, Sean is now a patrolman with the Boston Police Department, eager to uphold the Reagan legacy while forging his own path.

Danny also relocates to Boston and joins the local police force, creating a fresh on-screen dynamic: father and son serving in the same department for the first time. This new setup allows Danny and Sean to navigate the challenges of family life and police work side by side — territory they never explored during Blue Bloods.

“Really, it came down to we’re telling a new chapter in both of their lives. It’s not just Sean who has joined the family business as it were and is turning over this new leaf, but now Danny is the father to a cop, which he’s never been before,” Margolis explained to the outlet.

He continued, saying, “There are all these new storytelling lanes to explore. It felt like there was an organic opportunity to bring in a new performance with a new energy, to help dramatize that change. It is the same character, it’s the same relationship, but it’s also completely different.”

What was the fan reaction to the Boston Blue recasting?

Fans had mixed feelings about Amonsen stepping in to replace Terraciano as Sean in Boston Blue.

“There was absolutely no reason to recast him,” one user said in the Boston Blue Instagram comments. “The change does a real disservice to fans who have grown up alongside the original actor.”

Another user echoed that same sentiment, writing, “I miss the real Sean.”

Meanwhile, others filled the comments with praise for Amonsen and the uptick of father-son moments in the new series.

“The father/son interactions with Danny and Sean have been my favorite part of the series so far, and I hope these scenes continue!” one fan wrote on Instagram. “It’s great to see Danny adapting to being the father of a cop.”

What has Mika Amonsen said about the recasting?

Amonsen has acknowledged that his casting as Sean has drawn “some negativity” from fans, but he’s choosing to focus on the positive responses he’s seen on social media.

“When I look under those posts that have the negativity, there’s a lot of fans rallying for Sean and people saying that they really enjoyed this character that I’ve created — or my version of character,” he told Us Weekly in November 2025. “That makes me happy.”

Amonsen also admitted that stepping into Terraciano’s role came with “a ton of pressure.” To prepare, he binged Blue Bloods and made sure to preserve certain defining traits of Sean, like his hair styling and upbeat energy.

“I really want to maintain Sean as close as I can out of respect for this character that everyone loves — but also the character Andrew built,” the actor added.

What has Andrew Terraciano said about the recasting?

While Terraciano hasn’t commented on the Boston Blue recasting, he seemed at peace with closing the chapter on Sean when Blue Bloods finished filming its final season in June 2024.

“It feels like, after 15 years, ‘family’ isn’t a big enough word for all of the people at Blue Bloods that have changed me, and helped me, and grown with me,” he wrote on Instagram. “I am so unbelievably grateful to every single person that has guided me and provided me with wisdom and lessons that I will hold with me.”

He continued, writing, “To the cast and crew, tell everyone you can how fantastic this was, because it was fantastic, and consider this a formal thank you to each and every one of you. I look forward to seeing everything you all go out and do. Sean Reagan, I let you go.”