The One Chicago world is experiencing a big change: Matt Olmstead, an executive producer on the four series in NBC's interconnected Chicago franchise, will depart Chicago P.D. as showrunner after its currently airing fourth season, according to Deadline. There is no replacement set.

A key presence in the franchise almost since its inception in 2012, Olmstead joined Chicago Fire as an executive producer and showrunner before co-creating the police procedural spin-off with Dick Wolf.

Also an executive producer on Chicago Med as well as the franchise's latest entry, Chicago Justice, Olmstead is said to have departed under amicable terms and is likely to be fielding offers for a new overall deal.

How well do the stars of Chicago Fire, P.D., Med and Justice know the other shows?

TVGuide.com has reached out to NBC for comment.

Chicago P.D. airs Wednesdays at 10/9c on NBC.