Why does Boston Blue's Sean Regan star look so familiar? Here's where you have seen the actor before 

CBS' Boston Blue, the spin-off of the network's beloved police procedural Blue Bloods, premiered with a major recasting for Danny Regan's son, Sean Regan. The spin-off series marks Danny's (Donnie Wahlberg) new adventure in Boston, after he leaves his Regan family and takes up a job with the Boston Police Department.

While Boston Blue boasts a new ensemble cast, Danny's youngest son, Sean Regan, remains at the centre of the narrative and the reason for his father's shift to Boston. As seen in the premiere, after Sean badly injures himself during a call, Danny decides to stay by his side in the Boston police force.

Fans were certainly delighted to see Sean Regan's character debut as a police officer in Boston Blue, who was played by actor Andrew Terraciano in Blue Bloods. However, actor Mika Amonsen will play Danny's youngest son in the spin-off series.

You are certainly not alone if Sean Regan star looked familiar on-screen as Mika Amonsen has appeared in many TV shows and movies, including Reacher, Apple TV's Pachinko, Eli Roth's 2023 horror movie Thanksgiving and Corin Hardy's 2025 film Whistle.

More on this in our story.

Who plays Sean Regan on Boston Blue?

While Sean Regan's recasting in the Boston Blue premiere irked many Blue Bloods fans, the creators have set this character's fate in stone for the spin-off series. Canadian actor Mika Amonsen made his impressive debut as Sean Regan, Danny's youngest son in the Blue Bloods premiere.

Once Amonsen's Sean became familiar with the new surroundings, he started to fit into the show's Boston-set narrative. The premiere kicked off with Sean and his partner in action after they saved some civilians from a burning building.

According to Mika Amonsen's IMDB bio, he was not always interested in acting and instead took after his father's passion for music. Amonsen started playing the electric guitar at the age of 13 and eventually became a part of a local band that performed at large local venues.

However, Boston Blue star quickly pivoted to acting and had his first brief role in the 2017 American political thriller series Designated Survivor. On IMDB, Mika Amonsen is credited under many popular small-screen titles, including Suits, Good Witch, Slasher, Dare Me, Wayne, Murdoch Mysteries and The Spenser Sisters.

Additionally, Amonsen also had brief appearances alongside star Alan Ritchson in Prime Video's Reacher and Lee Min-ho in Apple TV's Pachinko, where he played the character of American G.I.

Why was Sean Regan's character recast?

In a recent interview with TV Insider, Boston Blue co-creators Brandon Sonnier and Brandon Margolis have explained their reasons to recast Sean Regan's character:

“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.''

While Sean Regan's Boston Blue character is the same as that of the parent series, his personality and ambitions have changed. They added:

''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.We wanted him to join the story in progress.”

While many fans have questioned this recasting decision, Mika Amonsen is a promising star. Blue Bloods' fans will certainly miss Andrew Terraciano's iconic run as the character from the parent series, but the spin-off will likely justify this recasting in the upcoming episodes.

Boston Blue releases weekly episodes every Friday on CBS.

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