Boston Blue's Big Switch: Why Sean Reagan Got a Whole New Look

Hey, Blue Bloods fans! The highly anticipated spin-off, Boston Blue, finally hit our screens, bringing back Donnie Wahlberg as Danny Reagan and introducing a whole new chapter. But there's one major change that's got everyone talking: Danny's youngest son, Sean Reagan, looks totally different! Andrew Terraciano, who played Sean for 14 seasons on the original show, has been replaced by Mika Amonsen. So, what's the deal?

TL;DR

• Boston Blue, the new Blue Bloods spin-off, premiered October 17, 2025.
• Sean Reagan, Danny's youngest son, has been recast with Mika Amonsen taking over from Andrew Terraciano.
• Creators say the switch was a creative choice to signal a "new chapter" for Sean as a cop and bring "different energy" to the role.

Unpacking the Creative Decisions Behind Sean Reagan's Recasting

Alright, let's get right to it. When Boston Blue was first announced, whispers started about a potential recasting, and now we know it's true: Andrew Terraciano is out, and Mika Amonsen is in as Sean Reagan. It’s a pretty big deal, especially since Andrew literally grew up on our screens for 14 seasons of Blue Bloods.

So, why the change? The show's co-creators, Brandon Margolis and Brandon Sonnier (affectionately known as "The Brandons"), have been pretty open about their thinking. Margolis told TV Insider, "We wanted a slightly different version of Sean. We wanted a character that feels familiar, an actor that does resemble the character that we watched grow up. But as you saw in the pilot, he has made some life changes and having joined the police force, he is really picking up that family mantle."

Essentially, they weren't just looking for a new face; they were looking for new energy to match Sean's new life path. Margolis elaborated in an interview with Variety, explaining that while they "love Andrew and the work he did over the years on Blue Bloods," the spin-off is about a "new chapter" for both Sean and Danny. It's not just Sean becoming a cop; it's also Danny becoming "the father [of] a cop, which he’s never been before." This, they felt, created 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. We love what Mika has brought to Sean, this vulnerability, yet this desire to prove himself. It’s just been great to watch it come to life."

— Brandon Margolis, Boston Blue Co-Creator

It sounds like they wanted an actor who could embody this new, more mature, and more vulnerable version of Sean, ready to step into the demanding world of law enforcement. Margolis even admitted to TVLine that it was a "gamble to open the show on a new face," but felt the story demanded an immediate connection, and Sean's heroic — though tragic — moment in the pilot was the perfect way to "pull Danny Reagan into this world."

Sean Reagan's New Career Path and Its Impact on Danny Reagan

One of the biggest plot twists (besides the recasting itself!) is Sean's new career. If you remember Blue Bloods, Sean was often seen as more artistically inclined, and even had a few rebellious moments, far from the straight-laced cop path. Now, in Boston Blue, he's a full-fledged Boston PD patrolman, dedicated to carrying on the Reagan family legacy, but on his own terms.

The premiere episode, "Faith and Family," really threw us into the deep end. We see Mika Amonsen's Sean already on duty, patrolling with fellow rookie Jonah Silver (Marcus Scribner). Things take a dramatic turn when they respond to a fire, and Sean gets seriously injured in an explosion while trying to save people. This incident, which puts him in the hospital, is what brings his dad, Danny Reagan, to Boston. So, not only is Sean now a cop, but he's also already been in a life-threatening situation, forcing Danny to confront the dangers of his son following in his footsteps.

This dynamic is a central theme of the spin-off. Danny, who reprises his role as a detective but now with the Boston Police Department, finds himself paired with Detective Lena Silver (Sonequa Martin-Green). But his primary motivation for staying in Boston is to be there for Sean. It's a new challenge for Danny to be the father of an active-duty cop, a role he's never experienced before, even with his other son, Jack.

Meet Mika Amonsen: The New Face of Sean Reagan in Boston Blue

So, who is Mika Amonsen, the actor stepping into such familiar shoes? Mika is a Canadian actor who actually started his creative career as the lead guitarist for a rock band in Toronto before transitioning to acting in the late 2010s. Talk about a career pivot!

He's got a pretty decent resume already, with roles in shows like Designated Survivor, Suits, and even the popular K-drama Pachinko. What's cool is that Boston Blue was filmed in Toronto, which happens to be Mika's hometown, making the gig a bit of a homecoming for him.

Mika understood the weight of taking on a role previously played by someone else for so long. He told TV Insider that it felt "surreal" to step into Andrew Terraciano's world, and he actually went back to watch Andrew's later episodes of Blue Bloods to study Sean's dynamic with Danny and his humor. His goal was to "carry over that warmth, his dad’s stubborn streak, and a quiet intelligence that really feels like a Reagan."

He also had nothing but praise for his new on-screen dad, Donnie Wahlberg. "Donnie is incredible! He’s full of energy, cracking jokes, and the second the cameras roll, he’s laser-focused," Amonsen shared, adding that Donnie was "generous" with advice on joining long-running franchises and made him "feel like family from day one." Sounds like a great working relationship, which is super important for a father-son dynamic on screen!

Fan Reactions and the "Gamble" of Recasting a Beloved Character

While the creators are confident in their decision and Mika Amonsen is clearly putting in the work, the recasting of Sean Reagan has definitely stirred up some strong feelings among the loyal Blue Bloods fanbase. The initial announcement sparked speculation and disappointment, and seeing a new face in the premiere solidified those mixed reactions.

Some fans, as seen on Reddit, were quite "upset that they made Sean a cop," pointing out that his character in Blue Bloods seemed to be heading in a different, more artistic direction. The sudden shift, without on-screen explanation within the spin-off, left some viewers feeling a bit "perplexed" by the character's new trajectory. One Redditor even stated, "The reason why he and his dad move to Boston is stupid. I don't see myself tuning in."

On the other hand, the show isn't without its early wins. Movieguide reported that Boston Blue is "already a hit with fans and critics, scoring a 100% on Rotten Tomatoes." However, it's worth noting that critical reception can sometimes differ from deeply invested fan sentiment, especially when a core character changes. Brandon Margolis acknowledged this potential backlash, calling the decision a "gamble." But, he believes that Amonsen's "youthful energy" and portrayal of Sean's "vulnerabilities" will help win over audiences.

It's always tough when a familiar face is replaced, especially after spending so many years watching a character grow. But the creators are banking on the new storylines and Mika's performance to make viewers "love him right away" and embrace this new chapter for the Reagan family.

What Else to Expect from the Boston Blue Universe?

Beyond the Sean Reagan recast, Boston Blue is bringing plenty more to the table. Donnie Wahlberg's Danny Reagan is definitely the centerpiece, but he's surrounded by a compelling new cast and some familiar faces from New York.

Here's a quick look at who's who in Boston:

• Donnie Wahlberg as NYPD Detective Danny Reagan (now Boston PD)
• Mika Amonsen as Sean Reagan (Boston PD patrolman)
• Sonequa Martin-Green as Detective Lena Silver (Danny's new partner)
• Gloria Reuben as Boston District Attorney Mae Silver (Lena's mother)
• Maggie Lawson as Police Superintendent Sarah Silver (Lena's sister)
• Marcus Scribner as rookie cop Jonah Silver (Lena's brother, Sean's fellow patrolman)
• Ernie Hudson as renowned Baptist pastor Reverend Edwin Peters (Silver family patriarch)

And for those hoping for more Blue Bloods connections, you're in luck! Bridget Moynahan is set to return as Danny's sister, Erin Reagan, in future episodes. Plus, we'll see Marisa Ramirez reprise her role as Maria Baez, Danny's new girlfriend, making "multiple appearances" throughout the season, which is exciting for those who shipped Danny and Baez for years!

The spin-off aims to expand the legacy of Blue Bloods while offering a fresh, human perspective on Boston's law enforcement and community. Anthony Hemingway, who directed the pilot, praised the creators for finding "the heartbeat inside of the badge" and keeping the themes of family and community strong. CBS is reportedly very supportive, trusting the showrunners' vision to tell a fresh story.

So, even with the big change in Sean Reagan, it looks like Boston Blue is set to deliver plenty of the family drama, police action, and character development that fans loved in the original series. It’s a new city, a new department, and a slightly new look for a familiar face, but the Reagan spirit is definitely still there.

Frequently Asked Questions About Boston Blue and Sean Reagan's Recasting

When did "Boston Blue" officially premiere?

Boston Blue premiered on Friday, October 17, 2025.

Where and when can I watch new episodes of "Boston Blue"?

New episodes of Boston Blue air on Fridays at 10/9c on CBS. You can also likely stream them on the CBS app or website after airing.

Why was Sean Reagan recast in the "Blue Bloods" spin-off?

Co-creator Brandon Margolis stated that the recasting was a creative decision to mark a "new chapter" in Sean's life as a police officer and to bring "different energy" to the character. They wanted an actor who could emphasize Sean's transition into adulthood and law enforcement.

What is Mika Amonsen's background?

Mika Amonsen is a Canadian actor who was previously the lead guitarist in a Toronto rock band before transitioning to acting in the late 2010s. He has appeared in various TV shows and films, including Pachinko, and researched Andrew Terraciano's portrayal of Sean to prepare for the role.

What is the TV rating for "Boston Blue"?

Boston Blue is rated TV14, similar to its predecessor, Blue Bloods.

Will other "Blue Bloods" characters appear in "Boston Blue"?

Yes! Donnie Wahlberg stars as Danny Reagan, and Bridget Moynahan (Erin Reagan) is confirmed to return. Marisa Ramirez (Maria Baez) will also make multiple appearances.

Sources

• Movieguide.org - "BOSTON BLUE Creator Defends Controversial Recast: ‘A New Chapter’" (Published: October 24, 2025)
• TV Insider - "‘Boston Blue’ Creators Explain Recasting Sean Reagan for ‘Blue Bloods’ Spinoff" (Published: October 20, 2025)
• Us Weekly - "‘Boston Blue’ Creators Explain Recasting Sean Reagan for ‘Blue Bloods’ Spinoff" (Published: October 20, 2025, by Kelli Boyle)
• TVLine - "Boston Blue: Why Blue Bloods Spin-Off Boston Blue Recast Sean Reagan" (Published: Oct. 21, 2025, by Joe Roberts)
• BollywoodShaadis.com - "'Boston Blue', Meet Cast Member Who Appeared In Lee Min Ho's 'Pachinko' Before 'Blue Bloods' Spinoff" (Last Updated: Oct 18, 2025, by Peuli Bakshi)
• News-shield.com (via BLOX Digital) - "Why Blue Bloods Spin-Off Boston Blue Recast Sean Reagan" (Published: Oct. 21, 2025)
• ScreenRant - "Why Boston Blue Recast Sean Reagan" (Published: Oct. 17, 2025)
• TV Insider - "Who Is Mika Amonsen? Meet the ‘Boston Blue’ Star Playing Sean Reagan" (Published: Oct. 17, 2025)
• Looper - "Boston Blue: Why Sean Reagan's New Profession Is More Puzzling Than Ever" (Published: Oct. 18, 2025, by Melissa Lemieux)