Fans saw some big news in the recent episode of "Chicago Fire" season 6. After bravely saving someone in need in "An Even Bigger Surprise", Lieutenant Matthew Casey (Jesse Spencer) got promoted to Captain of Truck 81.

Viewers know just how much he has given over the years, whether for the Chicago Fire Department or during his stint as an Alderman. Despite his reticence and aloof demeanor, Casey is known to be that stand-up guy who has always been there in every situation. Thus, one can say that he definitely earned that promotion. However, while it is good news for Spencer's character, that is not necessarily the case for his good friend, Kelly Severide (Taylor Kinney).

In the early days of the NBC series, there was a ton of tension between the two despite their knowing each other since their academy days. Now that one already outranks the other, they might butt heads again in the coming episodes.

As showrunner Derek Haas recently hinted, Casey's promotion will not only affect his relationship with his wife Gabriela Dawson (Monica Raymund), but it will also strain his friendship with Severide.

"What makes that [promotion] even more interesting is Casey [will be] outranking Severide for the first time in the show," he told TV Line, "and what that'll mean going forward is something we're going to play out over the course of Season 6."

Like Casey, Severide is also a lieutenant at Firehouse 51, but he is in charge of Rescue Squad 3. He is a great firefighter with notable observation skills that have come to the fore in several arson investigations. It could be bugging him why he has not gotten the same recognition Matt recently received.

For now, how Kinney's character will truly take Casey's promotion is up in the air. Regardless, things are expected to get heated between the pair next episode. The official episode 5 synopsis reveals they will argue over the best way to save a teenager entangled in barbed wire. Check out the trailer below.

"Chicago Fire" season 6 airs Thursdays, 10 p.m. EDT on NBC.