The Big Bang Theory may have had its curtain call – complete with Sarah Michelle Gellar cameo – two years ago, but the beloved sitcom hasn’t left our hearts or the cultural zeitgeist.

But, with such enduring popularity and more guest stars than you could shake a replica of Gandalf’s stick at, why did Big Bang Theory even end in the first place?

So the official story goes (via Deadline), the cast – including Jim Parsons (who played everyone’s favourite Sheldon Cooper), Kaley Cuoco (the sometimes awful, but always loveable, Penny), Johnny Galecki (long-suffering best friend and boyfriend Leonard Hofstadter), Mayim Bialik (awkward neuroscientist Amy Farrah Fowler), Simon Helberg (creepy mama’s boy Howard Wolowitz), Kunal Nayyar (astrophysicist and longterm single Raj Koothrappali) and Melissa Rauch (high-pitched wife to Howard, Bernadette Rostenkowski-Wolowitz) – were all having a normal day on set, filming season 12, when co-creator Chuck Lorre ushered them all into his office.

Here he gave the floor to Parsons, who announced to the group that this was to be his final outing on the show. Afterwards, it was over to Lorre to reveal that Big Bang Theory would not be going ahead without one of its core characters, and so season 12 became the final one there and then.

At the time, Parsons dedicated an emotional Instagram post to his co-stars and the fans.

“It is hard (really impossible, actually) to really accept that this is a picture of the first of the final 24 episodes we will shoot for The Big Bang Theory,” he wrote. “I feel very fortunate that we have another 23 episodes to shoot this season because I am hopeful that with each and every one, my level of REALLY accepting this fact will sink in.”

The actor also expressed “such intense gratitude” to the “devoted viewers” who, he said, were “the ACTUAL reason we have been graced with the opportunity to explore these characters for 12 years of our lives”.

Parsons has since revealed a bit more about his own personal decision to walk away from the hit sitcom.

“It was the first time in my life of doing this show that it occurred to me that I might want to not do another contract after [season] 12 was up,” he told The Hollywood Reporter when the finale episode aired.

“I don’t know if it’s because I’m an Aries or just because maybe I’m in touch with myself. Whatever it is, once I had that thought, I was like, ‘Well, that’s your answer,'” he added.

Parsons went on to add that there was “no factor” and “no situation” that had led to his decision, but that “when you know, you know”.

About two years later, Parsons opened up about having a particularly “dark” time in his life after season 11 of Big Bang, which helped shape his decision to walk away from the CBS comedy.

In a conversation on David Tennant Does a Podcast With…, the actor spoke about having been on “a complicated road”, touching on his exhausting work schedule, the death of one of his dogs, and an injury that happened while doing Boys in the Band on Broadway.

“I had this moment of clarity that I think you’re very fortunate to get in a lot of ways, of going: ‘Don’t keep speeding by.’ You know? ‘Use this time to take a look around.’ And I did,” he explained.

In 2020, while talking about how his role in Ryan Murphy’s Netflix miniseries Hollywood came about, he reflected on the period immediately after Big Bang Theory had come to a close.

“Ryan approached me at a time in my life and career where I had honestly no idea what was next or what I wanted to do,” the actor told The Globe and Mail at the time.

“It was only a few months after Big Bang had ended. I’m not going to tell you what I was looking for, because I didn’t know. I thought I’d know it when I saw it. Then Ryan came along and that’s all I needed to know.”

It seems as though Parsons wasn’t the only one ready for a change, as co-star Johnny Galecki had also dropped a hint that he would have been happy for season 12 to be the show’s last.

Back in 2018, Galecki had first sparked speculation that the series may have been drawing to a close by telling reporters at the TCA Winter Press Tour: “The only manner in which the cast has discussed wrapping [the show] has been that we’re all going to be very sad when that day comes… But I think at this point everyone’s very comfortable with 12 seasons being a good time to go home and see our families.”

Big Bang Theory was still hugely popular with audiences when its creators and cast chose to bow out. A ratings hit for CBS, it became the longest-running multi-camera series in television history. But the broadcaster had already launched a successful spin-off in prequel Young Sheldon – with Jim Parsons on board to narrate and executive produce.

Mayim Bialik more recently stirred up interest in the decision to finish Big Bang Theory, hinting that there may be more to the story.

“The way that I described the show ending was there are a lot of factors that the public doesn’t get to know about, about what goes into the decisions behind why a show doesn’t continue,” she told Us Weekly earlier this year.

Of course, this could be a reference to anything. We know (via Deadline) that renewal talks and negotiations between CBS, Warner Bros TV and the cast were said to have been ongoing at the time when Parsons and Lorre called time on things, but that doesn’t necessarily mean that a season 13 would have happened otherwise. As we know, there are lots of factors that tend to go into making renewal decisions.

Bialik painted a picture of a consensus though, revealing later in the interview: “I think, as someone who was grateful to work alongside Jim [Parsons] and eager to see the rest of what all of our lives held for us, I think there was a general feeling like it was time for us to move into something different.”

With the recent Friends reunion tickling our need for nostalgia, gossip around a Big Bang Theory one could step up – but Kaley Cuoco seems to think we might be in for a bit of a wait just yet.

It has only been two years, folks.

The Big Bang Theory aired on CBS in the US. You can buy the complete boxset now on DVD and Blu-ray.

This month, Digital Spy Magazine counts down the 50 greatest LGBTQ+ TV characters since the Stonewall riots. Read every issue now with a 1-month free trial, only on Apple News+.

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