Jim Parsons has opened up about moving on from The Big Bang Theory - which started its 12th and final season last night on RTÉ 2.

CBS and Warner Bros TV made the decision to send The Big Bang Theory to TV Heaven in 2019 when it became clear that Parsons - who plays Sheldon Cooper - was prepared to quit.

In the latest issue of Entertainment Weekly, the 45-year-old spoke about the reasons he was willing to walk away from the biggest TV show on the planet.

"It’s both as complex and as simple as just feeling innately that it was time. It speaks to a lot of things, none of them bad," he told Entertainment Weekly. "There is no negative reason to stop doing Big Bang.

Jim Parsons and Mayim Bialik in The Big Bang Theory

"It felt like we have been able to do this for so many years now, it doesn’t feel like there is anything left on the table. Not that we couldn’t keep doing it, but it feels like we’ve chewed all the meat off this bone.

"I guess at a personal level, it feels like the right time in my life. I don’t know what’s next for me. It’s not like there is something specific I am aiming for.

"I’m firmly in my middle age now. I don’t know how much longer I can wear [the T-shirts] without looking really long in the tooth. In a way, it’s exciting. What is this next chapter of life? What is this next chapter for all of us?"

"It will be very, very sad when it does end, even knowing [I am] okay with it. People are okay when they graduate but there are frequently tears at graduation. It’s hard to say goodbye to people that you have worked with for so long."

The Big Bang Theory continues on Thursdays on RTÉ 2