Sean Reagan will be accompanying his father, Danny, to Boston in "Boston Blue," but the series has recast the "Blue Bloods" spin-off's role - here's why.

Blue Bloods' viewers are finally getting an explanation for why Donnie Wahlberg’s character, Danny, moved in the 'Boston Blue' spinoff

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,