Moynahan will make a special guest appearance as Erin Reagan in the premiere and will also direct an upcoming episode of the spinoff

Donnie Wahlberg announced that his Blue Bloods costar Bridget Moynahan will guest star on his spinoff Boston Blue. Wahlberg and Moynahan played siblings Danny Reagan and Erin Reagan on the original Blue Bloods. Moynahan will appear in the premiere of the spinoff and direct another episode later in the season.

Bridget Moynahan is joining her brother in blue. The actress, 54, is officially set to return as Erin Reagan in the “Blue Bloods” spinoff, “Boston Blue.” The new show will follow Danny Reagan (Donnie Wahlberg) as he leaves the Big Apple to take a position with the Boston Police Department.