Heartbreaking reason why Jim Parsons left The Big Bang Theory after 12 seasons

While some sitcoms tail off in popularity until there's only the die-hard fans remaining, The Big Bang Theory was still drawing in huge audiences by the time it was over.

Among the main cast was Jim Parsons as Dr Sheldon Cooper, a character the show could not really do without, who decided to leave after 12 seasons in a move that signalled it was time for the sitcom to wrap things up.

During an appearance where Parsons was the guest on David Tennant Does a Podcast With... he explained that he decided he was going to leave the show after 12 seasons which was one of the driving reasons behind The Big Bang Theory ending.

After all, you can't really replace Parsons on the show and trying to plod on without one of the show's central characters rarely works in television.

They might say 'the show must go on', but it does eventually have to be over.

The Big Bang Theory ended in 2019 after 12 seasons. (Rich Fury/Getty Images)

Describing his decision to leave The Big Bang Theory as a 'complicated road, as you can imagine', he explained that he was 'exhausted' between his work on the sitcom and his other work.

It left him little time for his husband Todd Spiewak, and the actor remembered taking his ailing dog for a walk when he had to go and participate in a shoot for one of his other projects.

"I'll never forget that walk around the park to let him go to the bathroom before we went to the commercial shoot," Parsons recalled.

"He just looked so bad and I was so tired and Todd was like, 'We've got to go. We've scheduled this. They fit everything around your schedule.' And I just started crying.

"It makes me upset now. I was like, 'This dog's gonna die while I'm off working. I feel so bad'."

In the end the couple had to put the dog down, and along with the dog's passing and the exhaustion there was another major reason why the actor decided it was time to call it quits with The Big Bang Theory.

The actor had a few reasons why he wanted to leave the show. (Bruce Glikas/Getty Images)

He said: "My dad had passed years before, but he was 52. And I realised that at the end of season 12, I would be 46. I'm not superstitious or anything like that. It was just a context thing.

"I said, 'If you told me that like my father I had six years left to live, I think there's other things I need to try and do'. I don't know what they are, but I can tell that I need to try."

While The Big Bang Theory ended in 2019 after a dozen seasons Parsons continued to narrate the spin-off Young Sheldon until that concluded in 2024.

Since The Big Bang Theory ended Parsons has appeared in the Netflix series Hollywood, for which he was nominated for an Emmy, has appeared in films The Boys in the Band and Spoiler Alert and performed with Tennant in the TV series Staged.

He's also made a number of appearances in the theatre with A Man Of No Importance, Mother Play and Our Town, so it would seem that he's certainly been making the most of trying to do other things.