PEOPLE has an exclusive first look at next week’s episode of the NBC hit, featuring

the much-anticipated I dos — and a fond farewell Bells will be ringing on Chicago

Fire next week — but they won’t be calling the crew of Firehouse 51 to a local

disaster. It’s time for the wedding of two of their own: Sylvie Brett (Kara Killmer) and Matt Casey (Jesse Spencer). In an exclusive first look at a pair of their wedding photos, it’s clear their ceremony will indeed take place at The Aquarium (the fish store, not the Shedd Aquarium, as Brett had intended). The couple magically makes it work with moody purple lighting and gorgeous, large white flower arrangements. Standing before the happy couple is Chief Wallace Boden (Eamonn Walker), who will officiate. Brett’s Ambulance 61 partner, Violet Mikami (Hanako Greensmith), stands beside the bride as her maid-of-honor, while Kelly Severide (Taylor Kinney) is Casey’s best man.

Brett is wearing a floral lace gown with a sweetheart neckline and off-the-shoulder lace straps, while Casey is rocking a tuxedo. It appears they didn’t skimp on the cake either: The newlyweds are standing beside a sizeable four-layer, four-tiered confection. Given the brick wall behind them, the festivities may move from the fish store to Molly’s for the reception. The episode may be filled with cheers, but it’ll likely include some tears as well.

It marks Killmer’s final episode on the show, as Brett moves to Portland to be with her husband. Killmer joined the NBC hit in its third season in 2014 and her character soon became close friends with her fellow paramedic, Gabriela Dawson (Monica Raymund), who married Casey in season 5. The pair split in the premiere of season 7 when Raymund left the show. Spencer left the series in season 10 when his character moved to Portland, but has returned as a guest star for the wedding of Severide and Stella Kidd (Miranda Rae Mayo) later in season 10, as well as in season 11’s finale when he proposed to Brett. Still, as Boden says in the promo for the episode, “No matter how far you go, 51 will always be your home.