Change will follow Danny Regan (Donnie Wahlberg) to Massachusetts for his new “Blue Bloods” spin-off, “Boston Blue” — and not just because he’s in a new location. His son, Sean, will play a significant role in the series, but not with his original actor, Andrew Terraciano. Instead, Mika Amonsen, known for “Thanksgiving,” will take on the role. Since Sean has transitioned to a beat cop since his last appearance, producers wanted the character to have a refreshed appearance suitable for his new career.

Sean’s role as a cop seems to have influenced his environment. Recognizing his family’s esteemed policing history in New York City, Sean decided to start his police career in Boston, distancing himself from the familial pressures of being a Reagan with a badge. However, Danny soon makes a similar move and joins the Boston police, turning father and son into coworkers, reminiscent of Danny’s dynamic with his own brothers and father. This introduces a vital family connection in “Boston Blue” that complements the show’s premise. The strong family ties were a defining feature of “Blue Bloods,” distinguishing it from other shows and giving it engaging storylines.

While this setting allows Sean and Danny to bond like during the iconic Reagan family dinners on the original show, it also introduces inevitable tension between them. Sean must emerge from Danny’s shadow, whether this benefits or challenges him, while Danny needs to navigate letting his son find his own path. Although this provides compelling narrative material for “Boston Blue,” it doesn’t entirely align with what “Blue Bloods” fans would expect from Sean’s character arc.

For longtime fans, Sean becoming a beat cop is an odd choice for the character. During his time on “Blue Bloods,” Sean never seemed interested in law enforcement as a career choice — he instead expressed his love of art and a desire to become a firefighter. While he obviously loves and respects his family, when compared to his more staid and responsible brother Jack (Tony Terraciano), Sean is a rebel. Over the course of the series, Sean even runs afoul of the law multiple times for a variety of youthful mistakes, like skipping class, failing to study, and underage drinking. Ergo, making him a police officer like much of the rest of his family feels like an unexpected and disappointingly boring plot twist. 

Naturally, a son with a brand-new face won’t be the only challenge Danny Reagan will be forced to endure in Beantown. He’ll likely experience some pushback from his new partner, Detective Lena Silver (Sonequa Martin-Green), a cop who has her own long family history of upholding the law. He’ll also meet other members of the Silver family while working in Boston: Sarah (Maggie Lawson), Jonah (Marcus Scribner), and Mae (Gloria Reuben). Ernie Hudson will also appear as Reverend Peters when “Boston Blue” debuts on CBS in the fall.