Fans saw Captain Matt Casey decide to leave Chicago for three years to move to Oregon and help raise his late best friend's children, with him and girlfriend Sylvie Brett attempting to try long distance.
WATCH: Chicago Fire celebrates it's 200th episode with a big decision for Casey
"For over ten years you made this a special place," viewers saw deputy district commissioner Boden tell Casey at the end of the episode.
"Everyone you worked with on this shift, we got to call you brother. This place will never be the same and I thank you for your kindness, generosity and passion for this job. You will be dearly missed brother."
In the episode, Casey saved best friend Kelly Severide's life in his final fire, and Severide - played by Taylor Kinney - was near to tears as he said his goodbyes.
Jesse told press that his decision to leave comes after 18 years on network TV; he worked for eight years on NBC show House before helping to launch Chicago Fire.
Casey has left after 10 years
However he hinted that it won't be forever; he is expected to appear for the wedding of Severide and Stella Kidd. "I think it was pretty organic that he’s leaving and he’s going for three years but is he? We don’t know," he said.
"I realized I’d been doing TV for a long time, so I added it up… We were coming up on the 200th episode and I called Derek to break the news that it was time for me to leave the show.
"He agreed we should at least get Casey to the 200th episode. It was a difficult decision because I’ve loved the show from the start but there are other things I’d like to do in the future. There’s family I need to take care of, and 18 years is a long time."
However, Jesse hinted he may be back at some point
However, many fans took to social media to share their heartbreak and suggest that they would not be watching the show anymore.
"This is heartbreaking Jesse, can't imagine Chicago Fire without you, so no way I can keep watching. but I'm thankful for all these years and all the moments of joy you gave us. I'm gonna miss you so much," shared one fan.
He left to move to Oregon
Another added: "To say that I’m devastated to see you leave is an understatement. Casey has always been my fave from Day 1. You did an amazing job carrying this show as the lead and you’ll be sooooo missed! But I’m glad you did it on your own terms. Wishing you good luck in all you do!"
"Please tell me you are coming back!! Firehouse 51 will never be the same without Casey!!" commented another.
Taylor and Jesse celebrated 200 episodes with a special cake on set in Chicago
His co-stars also shared the love with Joe Minoso tweeting: "Brother. You are a beacon of leadership, friendship, professionalism and just an all around shining example of a man. You will be missed. Congrats on your exceptional work over 200 episodes."
"We love you forever, Casey/Jesse," added Hanako Greensmith.
One Chicago airs Wednesday at 8/7c on NBC
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