Fans of Blue Bloods were in for quite a shock last month when the new spinoff, Boston Blue, recast a role that was played by the same actor for all 14 seasons of the original.

Andrew Terraciano played Sean Reagan, son of NYPD Detective Danny Reagan (Donnie Wahlberg) in Blue Bloods; here, he’s now played by Mika Amonsen (seen in Reacher and Eli Roth’s Thanksgiving).

In Boston Blue, Danny Reagan moves to Boston to reconnect with his son, who is also now a cop, and to take a position at the Boston Police Department. The police procedural premiered on CBS on October 17.

Now that the series is well underway, the showrunners have shared why they opted to recast the role of Sean.

“Really, it came down to we’re telling a new chapter in both of their lives. It’s not just Sean who has joined the family business as it were and is turning over this new leaf, but it’s also now Danny Reagan is the father to a cop, which he’s never been before,” co-showrunner Brandon Margolis told Variety.

He said the recasting was “an organic opportunity to bring in a new performance with a new energy, to help dramatize that change.”

“It is the same character, it’s the same relationship, but it’s also completely different. We love what Mika has brought to Sean, this vulnerability, yet this desire to prove himself. It’s just been great to watch it come to life,” Margolis continued.

Margolis also told TV Insider that he wanted viewers to “join the story in progress,” with a new Sean already a full-fledged cop and continuing his family’s legacy of police work.

Boston Blue airs every Friday on CBS at 10 p.m.