"Chicago Fire" ended its third season with Severide (Taylor Kinney) being demoted, and Gabby telling Casey that she's pregnant. So what happens to these two characters when the show returns for its fourth season? 

Executive producer Matt Olstead told TVLine that Gabby's surprise pregnancy will not only change her personal life but her professional life as well. He told the website that a firefighter who gets pregnant cannot be assigned to work on the field. 

"The alternative is getting a desk job in the fire department while you're still pregnant," he said.

Olstead added that apart from the many things that Gabby is dealing with, she'll have to accept the fact that she won't be getting on a firetruck anytime soon. 

As for Casey, the EP said that although he and Gabby aren't together anymore, he'll go on protective mode and ask Gabby what she needs him to do, and whatever she decides, he'll "figure out his feelings about it later." 

Meanwhile, Severide's love life will also be featured in the upcoming season. After being with Shay, he has had a lot of relationships not only on "Chicago Fire" but also on "Chicago P.D." and "Chicago Med," but this time around, Olstead told TVGuide that he will have a new love interest, and he has his unexpected demotion to thank. 

"He's back to fling mode," said the producer.

Olstead revealed that as part of the consequences of being demoted, Severide has to undergo a manager trainee course where he'll meet the new lady in his life played by new cast member Rachel Nichols ("Criminal Minds," "G.I. Joe: The Rise of Cobra"). Nichols' character is said to be a "problem employee" at the law firm where she works, and a romance unfolds between her and Severide that will see complications in the future. 

"Chicago Fire" season 4 premieres on Oct. 13 on NBC.