[WARNING: The following story contains spoilers from Tuesday's Chicago Fire. Read at your own risk.]

Chicago Fire has said goodbye to another member of its team.

On Tuesday's episode, Peter Mills (Charlie Barnett) finally got his spot back on the squad — just as his mom and sister decided to take over his dad's restaurant in North Carolina. Despite saving a life on his first call back with the team, Mills realized it was time to choose his real family over his work one.

"I don't know if my dad expected me to follow in his footsteps," Mills tells Chief Boden (Eamonn Walker). "I do know he'd be proud that I did. I also know that he would've wanted me to live my own life, find my own path. I can't keep chasing his ghost. I want to be with my family."

Finale Preview: Scoop on 33 season-enders!

TVGuide.com chatted with executive producer Matt Olmstead to find out why the show decided to write out another main character leave and how it'll affect his partner Brett (Kara Killmer). Plus: Get some scoop on Casey and Voight's big finale showdown!

Why did you decide to have Mills leave the squad?
Matt Olmstead:
The hardest part of this job is when you feel it's the right time to make cast changes. It was solely based on bringing in new people for new stories. Otherwise it turns into a clown car. You have affection and admiration for [your cast], so you keep everybody, but it's at the detriment at being objective and making some tough calls in terms of storytelling. So, we wanted to shake things up and bring in a new character and we started discussing the idea ... and here we are. It was an extremely tough decision to make, but we feel good about it.

Why have him move away rather than killing him off?
Olmstead: His departure goes towards the original mythology we gave the character, which is that he had a dad die on the squad and his mom and sister had a restaurant. He worked at the restaurant and his mom didn't want him to be on the squad anymore, and he was pulled in two directions. Ultimately, he makes the determination that he fulfilled his father's legacy to the extent that he wanted to and he could check that box in terms of walking in the footsteps of his father who he never really knew.

Mega Buzz: Are Casey and Dawson getting back together on Chicago Fire?

I imagine his exit is the toughest on Brett going forward.
Olmstead:
She takes it the hardest — he was her first real partner. And she's not a thick-skinned, jaded paramedic who's been doing this a long time. She came from the sticks and she's still learning, so it hits her hard. Then, when he goes off, there are a few different moves within the department and we're bringing in a new partner for her who is going to be a great.

Can you say if her new partner will be a guy or girl?
Olmstead:
It's a girl.

I know Dawson and Casey aren't getting back together right now, but they're abnormally normal after that hookup.
Olmstead:
Well, if they're a perfectly happy couple there's nothing to write to. But if you break them up, you don't want them to hate each other. So, we wanted it to be somewhat amicable. Being friends first helps with having a foundation of sanity, and you can revert to that [after a break-up] if you're lucky. They had that, but there's also no denying they have real chemistry with each other. [In the finale] there are two cliff-hangers [and one] is between Casey and Dawson in terms of their relationship going forward and are they going to be together or not?

Severide (Taylor Kinney) and April (Yaya DeCosta) finally kissed! Is he ready to be in a relationship?
Olmstead:
[She] was one of those who got away. Strangely enough, it was like a version of the friendship with Shay (Lauren German), in that it wasn't romantic. They were friends. On the heels of the incident with Chicago Med, he [found] himself with her when all the defenses [were] down. Do they a chance? Maybe they'll always have Paris, we'll see. But that's where they're headed.

What more can you tease about the finale showdown between Casey and Voight (Jason Beghe)? Olmstead: It's pretty great because Voight appeared in the third episode of the first season of Fire and went nuts and they were mortal enemies. We've had other [characters] cross and bury the hatchet, but we've never had Casey with him intentionally. [Voight] has rehabilitated himself and apologized for what happened, but for Casey, the lengths that Voight went to get Casey to come off of saying his son was drunk when he crashed that car was unforgivable.

Finally, is anyone dying on this year's finale?
Olmstead: There is not a death of a character on either [Chicago Fire or Chicago P.D.].

Chicago Fire airs on Tuesdays at 10/9c on NBC.

Check out a tour of the set below: