As we head into the series finale of the record-breaking comedy series The Big Bang Theory, star Jim Parsons is opening up on his decision to leave the show. After 12 seasons on CBS, the hit show will air its final episode on May 16, but the popular series could have returned for at least another season. It all came down to Parsons, who was the one to make the decision not to return as Sheldon Cooper in a potential Season 13. Without Parsons, the choice was then made to end the series on a high note with the end of Season 12.

Recently speaking about what led him to walking away from the show, Jim Parsons simply reasoned that his heart just wasn't in it like it had always been before, which probably meant it was time to move on.

"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. 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.'

There was no factor; there was no situation that I was like, 'Well, I've had enough of that.' No. There was nothing like that. It was just...when you know, you know. And you're susceptible and thrown around by the whims of your own existence and getting to a certain age and your life changes and suddenly you just think different. It has been fascinating to think about who I was 12 years ago. And sometimes when I have trouble learning a line or saying a line of Sheldon's right now, it's hard to know why specifically. But it's like, you're not the same person you were. There is a possibility that this actually became more difficult for you in a way. And I don't know what that means but it's like you just change."

To be clear, it's not a decline in TV ratings or overall popularity that's putting an end to The Big Bang Theory. The series has achieved many tremendous accolades during its run, earning an astonishing 52 Emmy Award nominations. Ultimately, it would win ten of those, with four going to Parsons for his performance on the series. Ratings continue to remain very high as well, as the show is still TV's highest-rated comedy. With 24 episodes a season and 279 total episodes, the show also sets the record for the longest-running multicamera comedy series. There's still clearly money to be made by continuing the show, but it's certainly better to end it with Parsons gone than it would be to move on without him.

Related: Big Bang Theory Will End in 2019 with Season 12

The Big Bang Theory first premiered on CBS in 2007. It starred Parsons and Johnny Galecki as Sheldon Cooper and Leonard Hofstadter, two eccentric and nerdy physicists sharing an apartment in Pasadena, California. They live across the hall from waitress Penny (Kaley Cuoco), whom Leonard quickly takes a liking to. Aerospace engineer Howard Wolowitz (Simon Helberg) and astrophysicist Raj Koothrappali (Kunal Nayyar) also star as Sheldon and Leonard's closest friends. Later, Mayim Bialik and Melissa Rauch joined the main cast as neuroscientist Amy Farrah Fowler and microbiologist Bernadette Rostenkowski. Guest stars like Wil Wheaton and Sara Gilbert regularly appeared on the series as well.

Although the main series is ending, we haven't seen the last of the Sheldon Cooper character. The spin-off prequel series Young Sheldon stars Iain Armitage as a younger version of Sheldon, following him as a child in grade school. Parsons is still involved with the series as the narrator in addition to executive producing. The show has also proven to be a success for CBS, as the network renewed the series for two more seasons earlier this year. Its upcoming Season 2 finale, which will also air on May 16, will feature young versions of the other main characters from The Big Bang Theory.

For better or for worse, it's the end of an era for The Big Bang Theory. Ultimately, we will see if its predecessor Young Sheldon comes close to besting the record set by its parent series, but this is certainly going to be a major challenge for any show. This information comes to us from THR.

Jeremy Dick