Every year, television fans hold their breaths to see if their favorite shows will be renewed for another season. This year, procedural fans were eager to see if CBS would renew NCIS: Hawai'i after its freshmen season ended on a high note. To NCIS fans' delight, the new series was greenlit for a second season, but CBS also had some unfortunate news. Michael Weatherly's Bull would be ending after its Season 6 finale.Like The Rookie, Bull was loosely based on a true story. It premiered in 2016 and was inspired by its co-creator's (Phil McGraw) early career as a jury expert. In its titular role, Bull starred Michael Weatherly as Dr. Jason Bull, a psychologist and trial-science expert. He ran a company called the Trial Analysis Corporation (TAC), where his team of experts pooled their resources to become a formidable force in any courtroom. Now that the series has officially come to a close, here's a look at how and why Bull ended.RELATED: NCIS' Season 19 Finale Frames Parker for Murder

How Did Michael Weatherly's Bull End?

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Bull's final episode was a two-parter: "Silent Killer" aired on May 19, and "Goodbye" aired on May 26. In the episodes, TAC took on the defense of an apartment building owner named Ed Wilson. He was charged with poisoning multiple tenants with carbon monoxide. The case was proceeding as expected, but at the end of "Silent Killer," Bull figured out that Ed was guilty. In fact, he killed his tenants to cover up murdering a college student years before, which made him irredeemable.

There was a problem, though. Bull didn't have any evidence that Ed actually killed his tenants or the college student. He only knew because Ed admitted his guilt -- but Ed had done so in confidence. That meant that Bull was bound by attorney-client privilege and couldn't disclose Ed's murderous deeds to anyone outside of his team. That left TAC up the creek without a paddle.

Bull and his team spent all of "Goodbye" trying to find a loophole, but in the end, there wasn't a way to fix the problem. So, faced with the probability that a killer would walk free, Bull did something drastic. He burst into the juror’s room and told the truth. The judge declared a mistrial, meaning that Ed would be re-tried for his crimes. However, Bull's actions were a career-killer. He left TAC with Marissa in charge and began a new phase of life.

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Why Did Michael Weatherly's Bull End?

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Bull's first season commanded an impressive 11 million viewers per episode, but since then, that number had dwindled to 4.2 million. While that was quite the drop-off, Bull still outperformed other series in its time-slot. So, the decision to end the series wasn't about viewership; it was about Michael Weatherly.

Back in January, Weatherly announced the end of Bull on Twitter. He wrote, "Hello all! It's been my privilege to play Dr. Jason Bull but after 6 Seasons of incredible storylines, I've decided it's time to pursue new creative challenges and bring his story to a close." Not long after that, CBS confirmed Weatherly's announcement. So, from all appearances, Michael Weatherly was ready to move on, and CBS didn't want to renew the series without him. Of course, Weatherly's fans are hoping that his "new creative challenges" will include some kind of appearance on NCIS. While it seems like all parties are interested in the return of Tony DiNizzo, nothing has been confirmed, so NCIS fans will just have to wait and see.