Kaley Cuoco. Photo by Chris Pizzello/Invision/AP

Kaley Cuoco was left tearful after learning that 'The Big Bang Theory' will finish next May, as she was hopeful it would return for another instalment.

The 32-year-old actress - who has played the role of Penny since the series began in 2007 - is devastated that the hit CBS sitcom is coming to an end after 279 episodes as it has been life-changing for the star, but she's promised fans the finale will be "the best season" ever.

Alongside a professional photo of herself with some of her cast mates, Kaley wrote on Instagram: "This ride has been a dream come true and as life changing as it gets. No matter when it was going to end , my heart would have always been broken in two. Drowning in tears, we promise to bring you the best season yet. To the fans, our crew, families, Chuck Lorre, Warner Brothers , CBS, and everyone who has supported us for so many years, thank you. We are goin out with a bang @bigbangtheory_cbs (sic)"

Announcing the end of the hit show - which also starred the likes of Jim Parsons and Johnny Galecki - in a joint statement, Warner Bros. Television, CBS and Chuck Lorre Productions said: "We are forever grateful to our fans for their support of 'The Big Bang Theory' during the past 12 seasons.

"We, along with the cast, writers and crew, are extremely appreciative of the show's success and aim to deliver a final season, and series finale, that will bring 'The Big Bang Theory' to an epic creative close."

'The Big Bang Theory' is the longest-running multi-camera series in TV history and its final season is set to begin in the US in September.

News of the show's impending ending may have taken some fans by surprise after Kelly Kahl, CBS Entertainment President, recently revealed that the network was hopeful there would be another season.

Speaking at the Television Critics Association summer press tour earlier this month, Kelly shared: "We don't believe it's the final season.

"We are in preliminary discussions to renew the show with the studio that produces it, Warner Bros."

And Kaley had also expressed an interest in returning for a 13th season.

She said: "I love being a part of the show and I think it'd be really stupid to say no. There's just nothing better. Season 13 does sound kind of cool."

The final season of 'The Big Bang Theory' is poised to begin in the US on Monday, September 24.