Fans of the long-running series Blue Bloods were taken aback by the introduction of a familiar character in the new spinoff, Boston Blue. The series shifts focus to Sean Reagan, the youngest son of Danny Reagan, as he embarks on his journey with the Boston Police Department. A significant change in casting accompanied this development, as Andrew Terraciano, who portrayed Sean for 14 years in Blue Bloods, has been succeeded by Mika Amonsen to reflect Sean’s growth into adulthood.
Co-showrunner Brandon Margolis explained the rationale behind this decision, stating, “We love Andrew and the work he did over the years on Blue Bloods. It came down to we’re telling a new chapter in both of their lives.” Margolis emphasized that it’s not only Sean taking on the responsibilities of a law enforcement officer but also Danny stepping into the role of a father to a police officer, a scenario that brings fresh dynamics to the story.
Mika Amonsen, who previously appeared in projects such as Thanksgiving (2023) and Whistle (2025), steps into Sean’s shoes with a fresh interpretation. Margolis noted Amonsen’s portrayal brings a vulnerability and an eagerness to prove himself, saying, “It’s the same character, it’s the same relationship, but it’s also completely different.” The transition has not been without its detractors, as some long-time viewers expressed concern over the casting change. However, Margolis stood firm in his belief that finding an actor with a different energy was the right choice for the story being told.
Amonsen addressed the mixed reactions to his casting, acknowledging that while there has been some negativity, many fans have rallied around his version of Sean, expressing enthusiasm for the character’s new trajectory. He reflected on the pressure he felt coming into the role, particularly in wanting to honor Terraciano’s prior work. Through diligent binge-watching of the later seasons of Blue Bloods, Amonsen sought to understand Sean’s evolution and his dynamic with Danny.
In a show of support for the spinoff, Terraciano also expressed positivity about the transition, recognizing the value of new interpretations of beloved characters. “It’s beautiful because you’ll always remember every single line and every day that you had the opportunity to be that character,” he said. He made it clear that he was excited to see Amonsen bring new life to Sean Reagan.
This innovative approach to character evolution in Boston Blue aims to maintain the essence of the original series while providing viewers with a fresh narrative perspective. With the creativity of the showrunners and the dedication of the new cast, there is potential for exciting developments in Sean’s journey as he finds his place in the family legacy of law enforcement.