Andrew Terraciano will not return as Sean Reagan in the spinoff, and Mika Amonsen will now take his place in 'Boston Blue'

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,

Mika Amonsen will play Sean Reagan in the 'Blue Bloods' spinoff, 'Boston Blue,' a role previously played by Andrew Terraciano.