Blue Bloods' Season 11 finale was designed as a potential series finale

Deadline

Showrunner Kevin Wade was told before Thanksgiving that the Season 11 finale would comprise of two episodes airing back to back. So he assumed that the scheduling meant CBS planned to end the series. "Yeah, so I started to think about how do we do something that could serve as a season finale but also if need be as a series finale," he tells Deadline. "We went back to the end of the first season where all the Reagans became involved in finding out and catching and bringing to justice the bad cops who killed Joe Reagan who is of course, Joe Hill’s father. And it was kind of a callback to that, just in case it was a series finale it would have a circle to it."