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The role of Sean Reagan is in new hands in the Blue Bloods universe, and those behind the decision to recast the character are explaining why.

The first episode of Blue Bloods spinoff Boston Blue premiered on Friday, Oct. 17, and fans of the original series have been quick to spot the differences between the two shows — from an obvious new location for Donnie Wahlberg’s Danny Reagan to a new man playing his son Sean.

Indeed, Mika Amonsen has taken over the role of Sean Reagan from Blue Bloods alum Andrew Terraciano. PEOPLE previously confirmed the casting news back in July.

And in the premiere episode, Sean (now an ambitious rookie officer with the Boston Police Department) finds himself hospitalized after attempting to save civilians from a building fire. The blaze and its resulting injury inspire Danny to soon travel to Boston from his native New York, hence the show’s title.

But why did the team behind Boston Blue recast Sean? Co-showrunner Brandon Margolis told Variety that it only made sense given the character’s arc.

“We love Andrew and the work he did over the years on Blue Bloods. Really, it came down to we’re telling a new chapter in both of their lives,” Margolis, co-showrunner alongside Brandon Sonnier, told the outlet. “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.”

As Margolis explained, there are “new storytelling lanes to explore,” which felt like “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,” he said. “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 also told TVLine, in an interview published on Friday, that while he “loved” watching Terraciano “grow up on TV,” it “creatively made sense to find an actor with a different energy.”

“And to your point, yeah, it was a gamble to open the show on a new face — two new faces, actually — but the story required us to love him right away,” he said. “Opening with that heroic moment that has a tragic end was the right way to pull Danny Reagan into this world.”

Terraciano, 21, isn’t Wahlberg’s current on-screen son, but the actor still celebrated one of his life milestones earlier this year. Following Terraciano’s college graduation in May, Wahlberg offered his “congrats” on Instagram.

While Boston Blue kicked off with some new faces, fans of Blue Bloods were also treated to answers following the show’s 2024 finale. Specifically, the show revealed what’s gone down with Danny and his NYPD partner, Det. Maria Baez (Marisa Ramirez), since the events of Blue Bloods.

At the end of Blue Bloods, Danny invited his long-time partner to grab a pizza. And at the start of Boston Blue, the pair’s romance is basically confirmed. Danny is at his home (and shirtless) when Maria is shown by his side.

As Margolis told Variety, continuing Danny’s storyline meant looking at “what was owed” after the conclusion of Blue Bloods — including “what happened when they went out for pizza.”

“We really did want to feel like this show is continuing that story in fairly real time,” he said. “It’s going to be about a year since the finale was off the air, so if Danny and Baez were together, where are they at, and what would that look like? How could that potentially complicate a journey going from New York to Boston?”

He added, “It was important to us we pay service to that and continue to establish that relationship.”