Jim Parsons and Mayim Bialik in "The Big Bang Theory". Picture: Instagram

The 'Big Bang Theory' boss Bill Prady doesn't like to plan episodes so has no idea how the finale will pan out.

CBS announced last month that the US sitcom would conclude for good after the 12th season, but co-creator Bill Prady has admitted he's still unsure how the final episode will go because him and the writers prefer not to "plan ahead."

Speaking to UsMagazine.com, he said: "We're approaching the final season the same way we've approached the 11 seasons before: with no planning whatsoever. From day one, we have never planned an arch for a season. We don't plan ahead, we just kind of just tell the next story."

And, although he's still got another instalment to produce, Bill already knows he's going to miss the cast - comprised of Jim Parsons, Johnny Galecki, Mayim Bialik, Melissa Raunch, Kunal Nayyar, Kaley Cuoco, and Simon Helberg - because they all get on so well and have developed a strong friendship over the years. 

He explained: "I'm really, really gonna miss these people. It's a cliché to say everyone is friends and we all get along, but everyone is friends and we all get along and we all love each other. I will miss them very much."

And it's not just Bill who is upset over the forthcoming finale as Kaley - who has played the role of Penny since the series began in 2007 - recently said she was "drowning in tears" after hearing CBS' decision to pull the plug on the show. 

She said: "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)"

'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, 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."