The launch of Donnie Wahlberg’s highly anticipated Blue Bloods spin-off, Boston Blue, brought with it a familiar face in the lead, but one very surprising change to the Reagan family dynamic: the recasting of Danny Reagan’s youngest son, Sean Reagan. For 14 seasons of Blue Bloods, the character of Sean was belovedly played by Andrew Terraciano, who, along with his real-life brother Tony (Jack Reagan), quite literally grew up on screen.
When the Boston Blue premiere aired, fans were quick to notice that the new Sean Reagan, now a rookie officer in the Boston Police Department, was being portrayed by a different actor: Mika Amonsen. This decision, while a gamble given the character’s long history, was explained by the show’s creators as a creative necessity to signal a major new chapter in both the son’s and father’s lives.
The Creative Rationale: ‘A New Chapter’ Requires ‘New Energy’
The co-creators and showrunners of Boston Blue, Brandon Sonnier and Brandon Margolis (often referred to as “The Brandons”), addressed the casting change directly, explaining that the recasting was a deliberate choice tied to the character’s dramatic evolution and the new storytelling demands of the spin-off.
1. Sean’s New Role as a Cop
The central narrative thrust for Sean in Boston Blue is his decision to join the Boston PD as a patrolman, making him the fourth generation of Reagans to enter law enforcement. This is a massive life change from the high school and college student persona Andrew Terraciano portrayed in Blue Bloods.
Showrunner Brandon Margolis explained to TV Insider and other outlets, “We wanted a slightly different version of Sean. We wanted a character that feels familiar… 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.” This transition from a recurring child/teen role to a series-regular adult role required an actor who could immediately project the maturity, intensity, and vulnerability of a young man starting a dangerous career in a new city.
2. A Shift in the Father-Son Dynamic
The recasting also facilitates a profound change in the central relationship of the show: Danny Reagan is now the father of a cop.
Margolis noted that this creates “new storytelling lanes to explore,” and the change in actor was an “organic opportunity to bring in a new performance with a new energy to help dramatize that change.” While the character is the same, the dynamic is “completely different,” moving from a protective father-to-child relationship to a more complicated, high-stakes cop-to-cop dynamic. Mika Amonsen’s portrayal is intended to capture Sean’s “vulnerability, yet this desire to prove himself” in his new, heroic path.
The Impact on the Blue Bloods Legacy
Andrew Terraciano was a fixture at the famed Reagan family dinner for 14 seasons, appearing in nearly all 293 episodes of Blue Bloods. Growing up alongside his fictional father, Donnie Wahlberg, created a deep, genuine bond that resonated with fans. The departure is naturally difficult for the loyal fanbase to accept.
Andrew Terraciano’s Post-Blue Bloods Life
While the creative team’s explanation focused on the narrative, it’s worth noting the real-life circumstances of the original actor. Andrew Terraciano had been acting since childhood, dedicating over a decade to the role. By the time Blue Bloods concluded in 2024, Terraciano was focusing heavily on his college education and other academic pursuits, graduating in May of the same year.
Though it has not been officially confirmed whether Terraciano was offered the role and declined due to his academic focus or if the producers simply sought a fresh perspective, his focus on a post-acting future makes the creative decision more plausible from a behind-the-scenes perspective. Donnie Wahlberg even publicly congratulated Terraciano on his college graduation, demonstrating a continued warmth between the two, which suggests the split was amicable.
Mika Amonsen: The New Sean Reagan
Stepping into the role is Mika Amonsen, a Canadian actor who was cast as a series regular. Amonsen brings a different on-screen presence, which the showrunners clearly believed was necessary to embody a full-fledged rookie police officer.
Amonsen has expressed his awareness of the challenge, telling TV Insider that it was “surreal” to step into the role and that he studied Terraciano’s later episodes to carry over Sean’s “warmth” and “a quiet intelligence that really feels like a Reagan.”
Recasting: A Necessary Risk in the Spin-Off World
Recasting an established character is always a creative risk, especially one so integral to the original series’ history. However, in the realm of television spin-offs, it’s a practice often employed to serve a dramatic pivot:
- To Age a Character: When a time jump is required, a new actor is often used to quickly establish a character’s new, older age and life stage.
- To Change Character Trajectory: A new actor can signify a major psychological or professional shift, making it easier for the audience to accept the new version of the character. This is the primary driver for Boston Blue.
- Availability Issues: Original actors may not be available or interested in returning for a new contract, especially one that requires relocation (in this case, from New York to Toronto, where the new show is filmed).
In the context of Boston Blue, the new show is a universe expansion—it’s not simply a continuation, but a new story with a new setting and a new core ensemble (the Silver family, featuring Sonequa Martin-Green and Ernie Hudson). The decision to recast Sean Reagan with Mika Amonsen firmly entrenches the new show as an evolution, not just a reboot, helping to differentiate its tone and storytelling from its long-running predecessor while preserving the legacy of the Reagan name.
Ultimately, while the change was initially shocking, the explanation from the showrunners points to a clear and deliberate strategy: to use the casting as a storytelling tool to immediately establish Sean Reagan’s new adulthood and professional status, thereby creating a compelling new narrative for Danny Reagan as the father of a uniformed officer. The success of Mika Amonsen in winning over the millions of loyal fans will be one of the critical determining factors in the long-term future of Boston Blue.
