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,

CBS has officially greenlit Boston Blue, a Blue Bloods spin-off centered on Donnie Wahlberg’s character, Danny Reagan, and his son Sean. However, longtime fans may be surprised to learn that Andrew Terraciano, who played Sean Reagan across all 14 seasons of the original series, won’t be reprising the role.