The One Chicago universe is saying goodbye to another long-standing cast member.

Reports emerged Thursday afternoon that Kara Kilmer will be stepping away from her Sylvie Brett role during Chicago Fire Season 12.

While we know Kilmer will be back for some episodes, it has not been determined how long she'll be sticking around.

The news is undoubtedly a huge blow to fans, but it could indicate that happiness could be in the cards for Brettsey.

Chicago Fire Season 11 in shocking fashion with Brett's on-and-off boyfriend returning to Chicago and popping the question.

At the time, fans thought it could indicate that Jesse Spencer could be staging a more permanent return to the show.

Now, it seems he was back to help set up Kilmer's final arc.

If you watch Chicago Fire online, you know Bretty and Casey's relationship has featured several bumps in the road, but their undeniable bond always brings them back together.

Brett was initially unsure about moving away from Chicago with Casey, but if they do make it down the aisle, there's a good chance Brett will agree to move elsewhere.

This is all speculation, assuming that the pair do indeed get engaged.

Chicago Fire likes to keep viewers on their toes, so Brett's final arc may go in a completely different direction.

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We'll have to tune in when the show hits the air again.

Chicago Fire was one of many shows impacted by the dual Hollywood strikes and isn't expected to resume production for another couple of weeks yet.

NBC has also yet to confirm when the show will be back, but if we had to guess, the show will launch in late January or early February 2024.

Kilmer joined the Chicago Fire Season 3 cast as a replacement for Lauren German's Leslie Shay, who died the previous season in an accident.

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She had various memorable storylines throughout her time on the show, and truthfully, there's a good chance she'll pop back up down the line.

The series likes to bring back its most popular cast members, even if it seems they're done with the show for good.

It is unclear whether Kilmer was ready for change or if creative reasons drove the decision.

Looking ahead to Chicago Fire Season 12, it will be under the leadership of Andrea Newman, who will serve as the sole showrunner following Derek Haas' exit.

It was revealed earlier this year that Taylor Kinney would be staging a comeback as Kelly Severide.

Kinney was written out of the show earlier this year due to a personal matter and will be back on the air at the beginning of the season.

Unfortunately, we don't know whether he'll be a guest star or series regular, but we should get more indication when the show returns early next year.

Chicago Fire will have a shortened season due to the delays brought on by the strike.

In other One Chicago news, Tracy Spiridakos is departing Chicago P.D. as Hailey Upton.

The expansive Dick Wolf universe is also saying goodbye to Jeffrey Donovan, with the actor being written out of Law & Order.

There's a good chance there will be more high-profile casting shakeups as the broadcast networks get their returning shows into production.

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For now, all we can do is speculate about what will become of Brett.

What are your thoughts, TV Fanatics?

Hit the comments.

Paul Dailly was an Associate Editor for TV Fanatic.Follow him on X.