“Chicago Fire”'s Kara Killmer Opens Up About the Brettsey Wedding and Saying Goodbye to Sylvie (Exclusive)

Sylvie Brett's "getting everything that she always wanted," the actress tells PEOPLE

Chicago Fire said goodbye to one of its own Wednesday night — in the most joyful way possible.

Sylvie Brett (Kara Killmer) and Matt Casey (Jesse Spencer) were married in a surprisingly beautiful wedding set in a fish store, followed, naturally, by a reception at Molly's. Shortly after that, they headed off to Portland, together.

Meaning, yes, it was Killmer's final episode 10 years after her first. And, for the actress, leaving on that beautiful note was a full-circle journey.

When Sylvie Brett became a paramedic at Firehouse 51 in 2014, she was a bride who'd just been left at the altar by her high school sweetheart. "Then we finish with her standing across the aisle from the love of her life, getting married and finally getting everything that she always wanted," Killmer, 35, tells PEOPLE. "I could not ask a better conclusion for Sylvie."

Related: Chicago Fire's Brett and Casey Tie the Knot in a Fish Shop-Set Wedding: Get an Exclusive First Look

"You are my port in the storm," Casey said in his vows. "The most generous, caring person I've ever known — and sometimes the most stubborn. ... This, the two of us together, is a fire that will never go out."

As their Firehouse 51 family laughed, Matt added: "I had to get a fire metaphor in there somehow."

Sylvie's vows began: "Here's why I wanted to get married in the aquarium: Years ago, you and I took Amelia to go and see the fishes there, do you remember? What you don't know is that is when I realized that you are the only man for me. ... I knew you were born to be a father. And when you decided to be a father to the Darden boys, it only made me love you more, even though I was trying so hard to let you go. And I couldn't. It's like you said: we were meant to be. We were meant to be a family."

Below, Killmer shares all the details of wedding dress shopping for Sylvie, her final moments on set and the advice she'd give to the next actor stepping into Ambo 61.

PEOPLE: How are you feeling knowing your final moments of Chicago Fire are about to air?

KARA KILLMER: It's honestly been a lot of fun. I'm probably two weeks from what was my last day on Fire, and I just got together with Hanako [Greensmith, who plays Violet Mikami] and Miranda [Rae Mayo, who plays Stella Kidd] to watch episode 5, and we're still talking frequently. So it's bittersweet, but it's more sweet than bitter.

Let's talk about the wedding itself. What were your first thoughts when you saw the fish store?

I walked in and was like, "Yeah, they have their work cut out for them. This is an uphill climb." It's a beautiful shop and all of the fish are so gorgeous, but it's kind of the perfect challenge for 51. I mean, this is a staple of our show: somebody has a problem, and 51 binds together and pulls out all the stops to come up with a solution.

Related: Everything to Know About Chicago Fire Season 12

And when you saw it decked out for the ceremony?

It looked like a different place, for sure. It was very interesting to see how they tweaked everything to make it look like a venue. I told the owner of Tank It Easy, which is the real name of the aquarium, "You're probably going to get requests after this to be a venue for weddings, so don't forget how you rearrange things."

Tell me about finding Sylvie's dress. What was that experience like?

So fun. The wardrobe director, Sue Kaufmann, and I basically went on four dates around the city to different bridal shops. I probably tried on about 50 dresses. We found five of them that were our top picks, and then she brought those into the studio and we actually had a little bridal party. Hanako and Miranda came in, my makeup artist Karen [Brody] came in, and I tried on all the dresses and got all their input. It was like Say Yes to the Dress. The resounding feedback was to choose the one that we landed on. It's very Sylvie. It's very wistful and romantic, and the flowers are very spring-like. I wore pale pink shoes underneath. I was having a Barbie moment.

So was the wedding itself your final days on set?

My final day on set was actually the reception at Molly's, so it was one big party. I kind of love that. The very last scene that I got to shoot, I was wearing a wedding dress. It was like, "Well, I couldn't feel more beautiful than this." It was a lot of fun. It was a perfect way to close out my experience and to finish out Sylvie's storyline.

Related: Taylor Kinney to Return to Chicago Fire in Season 12 Following Hiatus

When you heard, "That's a wrap on Kara Killmer," were there tears? How did that feel?

It was kind of surreal. There's so much buildup. We had been coming off of this long strike and coming back for six episodes, so I had a lot of time to process it, and I would say I spent more time savoring it than grieving. Ten years is a long time, and I just had the best time that I could possibly have. I did break down at one point when our paramedic technician, Michelle Martinez, who's a real Chicago Fire Department paramedic, she's been consulting on the show since season 1, gave me a necklace with a replica of the Chicago Fire Department badge, and it has Sylvie's badge number on it and her badge number on it. She gave it to me with the EMS prayer, and it was incredibly thoughtful.

That is really cool. Tell me about the decision to leave. Did you know when the proposal happened at the end of the last season?

The writing's been on the wall for a long time. Sylvie and Matt, their saga, that relationship had been building up for three years, and then Jesse exits the show [in 2021]. She tries to do long distance and she tries to let Matt go, and she dates Dylan for a little bit. And then at the end of last season, she obviously very suddenly steps into being an adoptive mother, and [she and Matt becoming a family] is for sure the most natural, inevitable conclusion for the arc of her character.

So what's next for you?

Next I'm just going to run headlong into auditioning, and I know there's a lot of interesting projects out there. I'm excited to try something new. It's been so humbling and so satisfying to get to play a first responder for 10 years, but I'm excited to try something different. It's time to see what else is out there, but I'll definitely be taking a little bit of the magic that I've learned on Chicago Fire and through Wolf Films with me to whatever set I step onto next.

Related: How 'Chicago Fire' Stars Taylor Kinney and Joe Miñoso Keep It Sexy, from Zumba to Big Macs

The departure of Brettsey is going to leave a sense of emptiness for their shippers. Who do you think is the show's next big ship?

Oh my goodness. I mean, I feel like I am leaving as the captain of the Mikarver ship. You just never know what might be bubbling with Violet and Carver [Jake Lockett]. But I would love for Hanako to get to play a great romance.

What advice do you have for someone filling your shoes and joining Ambo 61?

My advice would be you have to fall in love with the first responders. You have to pay attention to all of the real first responders that we work with every day. If you can't be enamored with the fact that you're getting to play an everyday hero, then it's just not going to land. But if you can really appreciate and admire what these servicemen and women are doing every day, then there's a place for you.

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Chicago Fire airs Wednesdays at 9 p.m. ET/PT on NBC.

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