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

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,

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.