Mika Amonsen will replace Andrew Terraciano, who played Sean Reagan throughout the 14-season run of "Blue Bloods."Though Donnie Wahlberg is the only member of the core Blue Bloods cast set to return for the long-running series' first spinoff,

Although “Boston Blue” is a direct offshoot of “Blue Bloods,” the Reagan family will look a bit different this time around. Mika Amonsen has joined the CBS drama in a series regular role playing the youngest son of Donnie Wahlberg's character,

As for Amonsen, he has previously starred in an episode of Apple TV+'s Pachinko, Suits and Designated Survivor, as well as 2023 slasher Thanksgiving. The original series saw the role of Sean played by Terraciano, with the other Reagan son, Jack, being played by Andrew's real-life brother Tony.