The latest Boston Blue casting announcement is good news.
Star Donnie Wahlberg recently took to Instagram to share that Blue Bloods’ Erin Reagan would make a guest appearance in the spinoff’s premiere episode.
That answers one question: Will Boston Blue be more than tangentially related to Blue Bloods?

Why I’m Not Completely Surprised by This Boston Blue Casting Announcement
Boston Blue may be a spinoff, but it’s also a new show in development, and those often change as they get closer to production.
It was only a year ago that Georgie & Mandy’s First Marriage was set to premiere, with plans to include only one member of the Young Sheldon cast, which quickly changed. I figured Boston Blue would do something similar.
Of course, the decision to recast Sean ignited more than enough doubt and confusion.
That often works better in soap operas than established shows, and some fans were vowing never to watch Boston Blue because of it.

Still, the announcement that Erin will guest star in the first episode follows the same pattern as the casting news from Georgie & Mandy’s First Marriage, and I won’t be surprised if other Blue Bloods characters show up from time to time.
Tom Selleck has already expressed interest, and it would make sense for Frank to have a working relationship with the head of the Boston PD.
If Frank were to intervene in Danny’s career change, it would make for an interesting parallel with the premise that Danny moved to Boston to keep an eye on Sean.
Erin’s Inclusion Suggests a Proper, Reagan-Focused Goodbye for Danny

If Erin is in the premiere episode, it means one of two things.
Either Danny will say goodbye to his family in New York before the episode begins, or Erin will visit him in Boston.
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It’s more likely to be the latter because otherwise the entire Reagan family would appear in the premiere, and right now it’s just Erin.
I’d love a proper pilot, though, with one last look at the Reagans before Danny goes off into his own show.

That’s what would have happened if CBS had planned a spinoff before Blue Bloods ended instead of after the fact, and it’s the very least that the iconic series deserves.
Why Erin, Though? (And Will She Be a Regular?)
Although Erin was a beloved member of the Reagan family, she was often cast in a semi-antagonist role.
As the district attorney, she had to follow rules that often meant arrestees were released pre-trial, charges were dropped or bargained down, or evidence was deemed inadmissible.
That makes her an odd choice for the character who serves as a bridge between Blue Bloods and Boston Blue.
Additionally, fans are eager for information about Jamie and Eddie’s baby, who was due to be born on June 13, 2025, according to the Blue Bloods series finale.

Erin’s inclusion will probably show off her sisterly side more.
She and Danny were often at odds on Blue Bloods for professional reasons, so it’ll be great — and preserve that all-important family feeling — for Erin to help Danny settle in.
Since Sean is becoming a cop in Boston, Erin might also be there to support his career. It would also be great if Nicky had moved to Boston, too, so that Erin has an additional reason to visit.
Unfortunately, Erin will not be a regular — her current billing is as a guest star.
Storywise, this makes sense.

Erin is an assistant district attorney in Manhattan, and the premise would turn into a parody of itself if there were a mass exodus of Reagans to Boston, all with parallel jobs to the ones they held in New York.
That said, Boston Blue would be wise to make Erin, or other Reagans, recurring parts of the cast rather than writing them out altogether except for occasional cameos.
While Erin’s inclusion in the pilot is great news, there’s a risk that some of Blue Bloods’ most loyal fans will see her appearance as a gimmick designed to get them to watch a series that isn’t the one they long for.
We’ll let you be the judge on that.

We want to hear from you about this!
If you’re a Blue Bloods fanatic, hit the comments with your thoughts about this news. Are you likely to watch Boston Blue?
Let’s get a robust conversation going. Invite your fellow Blue Bloods Fanatics to join in the fun, too!
Boston Blue will premiere on CBS on October 17, 2025, at 10/9c. In the meantime, all 14 seasons of Blue Bloods are available to stream on Paramount+.
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