Let the guessing games begin, Chicago Fire Fanatics.

And break out those tissues.

Speaking to TV Guide, showrunner Matt Olmstead has confirmed that the explosion which rocked Firehouse 51 on the Chicago Fire Season 2 finale will claim the life of at least one key individual.

"Not everybody makes it out of that building," Olmstead says. "And then certainly what people deal with in terms of the loss of whomever that character is, that's definitely what we're dealing with in the first episode and beyond."

It sounds like Yuri Sardarov’s Otis will return for certain, but nearly everyone else is up for grabs, with the deceased’s identity being revealed early on the September 23 opener.

Over the past couple years, Andy Darden, Hallie Thomas and Rebecca Jones have all passed on, but Olmstead promises the upcoming death will be the hardest for fans to take.

"This will be the death of a character that you're much more invested in," he says. "It's this family that takes a hit, and how do you come back from it? It's been done before, but not to this extent. ... The loss of a main character is a big deal."

Who do you think it will be?

Sound off now with your theories and go watch Chicago Fire online if you need to catch up prior to the fall premiere.

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.