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How Big Bang Theory stars were convinced to return to spin-off Stuart Fails to Save the Universe

The multiverse is full of surprises – with major stars from The Big Bang Theory making a surprise return to the franchise.

Bert, Stuart and Denise wear dark green military-style garb in a drab location, as they look irritated at someone in their group

Colin Remas Brown / HBO Max

Published: Friday, 31 July 2026 at 3:00 am

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The Big Bang Theory spin-off Stuart Fails to Save the Universe is definitely full of surprises – and within just two episodes, some of the original cast members have already returned to their characters to get in on the fun and bizarre series.

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The new, parallel universe-bending show opened with the shocking return of Kunal Nayyar’s Raj Koothrappali – albeit a dishevelled, paranoid and slightly feral version of him as he hides away during the apocalypse – but episode two upped the ante even further, with a surprise appearance from Kaley Cuoco.

Best known for her role as Penny, the beautiful and kind-natured next door neighbour who becomes part of Big Bang’s central nerdy gang, this time she enters the lives of Stuart, Kripke, Bert and Denise as a rebel leader in one of the show’s many alternate universes.

While others have made cameos in spin-off Young Sheldon, neither Nayyar nor Cuoco have reprised their roles in the seven years since The Big Bang Theory ended.

Speaking to Radio Times about their surprise drop-ins, Kevin Sussman, who leads the cast as Stuart, said: “I was just delighted. I wasn't counting on anyone coming back, because they all have moved on, you know?

“I mean, they've all done how many episodes of the original? It's definitely over 200 I think, which is crazy. I was on it a lot, and I don't even know if I'm in a third of them!”

The Big Bang Theory ran for 279 episodes, of which Sussman appeared in 84 as down-on-his-luck comic book store owner Stuart – a character initially brought in as a foil for leading man Leonard Hoffstadter (Johnny Galecki) in his pursuit of Penny.

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However, over time Stuart – and his comic books – turned into a safe space for the beloved main gang (especially when they wanted to feel better about themselves, as Stuart always seemed to have it worse).

“We were all really tight on the show, so it was just such a pleasure,” he said of the main cast’s appearances. “It's been like seven years, I think, since the end of the original when we started, and so just seeing them, and they're all off doing their [own thing], they've all got their lives and stuff and so coming back and it was kind of like a wonderful reunion.”

“It’s just amazing how everybody slipped back into [it],” he added. “I mean, they're obviously playing alternate versions of their characters which was so fun, and the ones that have appeared so far, they were so game for it, and they all crushed. They were all so funny, and they sort of elevated everybody else on the set because they were so good.”

The main characters in The Big Bang Theory sitting and laughing in the show's living room set, eating takeout food.

(L-R) Melissa Rauch, Simon Helberg, Johnny Galecki, Kaley Cuoco, Jim Parsons, Mayim Bialik and Kunal Nayyar in The Big Bang Theory. Michael Yarish / CBS via Getty Images

In each episode, Stuart, alongside other recurring Big Bang Theory characters Bert (Brian Posehn), Kripke (John Ross Bowie) and Denise (Lauren Lapkus), are sent to alternate universes in a bid to track down a way to stop theirs from ending.

Episode 2 saw them enter a too-perfect utopia version of Earth, where they discover an AI overlord has taken over and citizens are microchipped in their brain stem to stop aggressive behaviour – forcing everyone to remain compliant, friendly and agreeable, even if they don’t want to.

Penny, with a rebellious streak seemingly no matter what universe she’s in, has formed a militia alongside her Big Bang beefcake ex-boyfriend, Zack (Brad Thomas Smith).

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While the appearance was short but sweet, fans were delighted to see a different side to Cuoco, and blows the door wide open to any other potential appearances as the rest of the season plays out.

Seeing as Leonard and Sheldon (Jim Parsons) were the ones responsible for the quantum machine that kicked off Stuart’s whole mess, are they next in line?

Guess we’re going to find out soon enough…

Stuart Fails To Save The Universe is available to stream exclusively on HBO Max from July 24 in the UK and Ireland.

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Authors

Tilly PearceFreelance Writer

Tilly Pearce is a freelance TV journalist whose coverage ranges from reality shows like Love Is Blind to sci-fi shows like Fallout. She is an NCTJ Gold Standard accredited journalist, who has previously worked as Deputy TV Editor (maternity cover) at Digital Spy, and Deputy TV & Showbiz Editor at Daily Express US.

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