Who is Mika Amonsen? Everything to know about the actor as he joins Boston Blue Season 1 as Sean Reagan

Longtime Blue Bloods fans were in for a surprise as its spinoff, Boston Blue, Season 1, premiered on October 17, 2025. While the central protagonist, Detective Danny Reagan, played by Donnie Wahlberg, remained the same, his son, Sean Reagan, had a new face. Played before by Andrew Terraciano, Sean was recast with Mika Amonsen, bringing in a new approach to the character.

Meanwhile, Boston Blue Season 1 is set to present NYPD Detective Reagan collaborating with Detective Lena Silver of the Boston Police Department. The other prominent characters that Wahlberg’s Danny gets to meet are Boston District Attorney Mae Silver, Police Superintendent Sarah Silver, Baptist Reverend Edwin Peters and rookie Jonah Silver.

With Sean getting caught up in a fire accident, Danny decides to stay in the city for as long as his son needs him. While this gives Detective Danny an opportunity to bond with his younger son, it also exposes him to some crimes that he feels obliged to investigate on the CBS procedural drama.

A glimpse at Mika Amonsen’s career

As mentioned before, Mika Amonsen stepped into the role of Sean Reagan, the younger son of Det. Danny Reagan of the NYPD. Mika is a Canadian actor. His dancer mother and music enthusiast father encouraged his interest in music and Mika took to an electric guitar at the age of 13. He soon joined a band that gave him opportunities to play for Canadian acts, at large venues and record for track albums.

After high school, Mika joined a university for higher studies. However, his interest and fascination for actors like Christian Bale, Heath Ledger and Tom Hardy drove his friends and family to encourage him to follow his dream. As such, he signed up with an agency and enrolled in acting classes. He soon received audition offers and projects.

Some of his noteworthy projects include television series Good Witch, Hudson & Rex, The Republic of Sarah, Murdoch Mysteries, Reacher, EZRA, Pachinko and more before landing his role in Boston Blue Season 1. Mika also appeared in the horror movies, Danger Next Door, Thanksgiving, Whistle and more.

Boston Blue Season 1: Why was Sean Reagan recast

As mentioned before, Sean Reagan was originally played by Andrew Terraciano in Blue Bloods. However, the production team decided on a recast for the spinoff, Boston Blue Season 1, with Mika Amonsen. 

Brandon Margolis, co-creator of the spinoff, told TV Insider that they were looking for a slightly different personality for Sean. While the viewers must find the character familiar, Sean must portray his new personality after he joined the Boston PD as a rookie. He explained the recast with the change in the version:

“…he has made some life changes and having joined the police force, he is really picking up that family mantle.”

While speaking to Variety, Margolis emphasized that they loved Andrew and his work on Blue Bloods. However, the recast is about a new chapter in Sean’s life that would also reflect in Danny’s relationship with his cop son.

“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.”

Boston Blue Season 1: How was Mika’s Sean introduced

On October 17, 2025, the premiere episode of Boston Blue Season 1 showed rookies Mika and Jonah hanging out when they witnessed a fire breaking out in a building. True to their profession, the young cops jumped in to save as many lives as they could. In the process, they got injured. Mika’s Sean passed out from his injuries, landing him at the hospital.

Detective Danny promised to stay in town to care for his son. As such, the episode ended with Sean waking up in his hospital bed to find his father at his bedside. Danny will likely investigate many Boston crimes while his son recuperates before joining girlfriend Maria Baez in New York.

Catch Boston Blue Season 1 every Friday on CBS.