Kaley Cuoco's Young Sheldon Role Confirmed: The Inside Story Behind That Big Bang Theory Easter Egg

The Big Bang Theory‘s Sheldon and Penny were (sort of) reunited in a recent episode of Young Sheldon — but you might have missed it if you weren’t listening carefully.

TVLine can now confirm that Kaley Cuoco made an uncredited, voice-only cameo in the prequel series’ Dec. 12 episode, “Teenager Soup and a Little Ball of Fib.” In the episode, Sheldon had a nightmare about an impending swim test in gym and found himself taunted by the bacteria-infested pool.

“That was absolutely the voice of Kaley as pool water,” series co-creator Steve Molaro told TVLine with a laugh. “I needed someone to do the voice. I knew I wanted it to be female and kinda sexy, and I said, ‘Well, duh! Kaley is perfect for this.'”

Once Molaro knew he wanted Cuoco, he phoned his former star to get her take on the peculiar part. “I said, ‘Hey, I have a weird pitch for you: Sheldon has a nightmare, and he has to go to this pool, and he speaks to the pool water. Do you want to be the voice of pool water?'” Molaro recalled. “She just laughed and said, ‘Absolutely, I do.'”

After Cuoco agreed to the cameo, she and Molaro discussed whether or not they wanted CBS to promote it ahead of time. “Sometimes I feel a little weird about things being over-promoted,” Molaro said, “and as awesome as it was, I don’t know that that should be the kind of thing that appears in promos. [Kaley] wanted to hold it under wraps [as well], so that if you figured it out, that was a little Easter egg for you, so we were all on the same page about that.”

Cuoco was the first of Jim Parsons’ former Big Bang Theory co-stars to cross over to the single-camera offshoot, on which he serves as narrator and executive producer. Iain Armitage, who plays the pint-sized boy genius, previously popped up in a final-season episode of The Big Bang Theory alongside Lance Barber (George Sr.) and Montana Jordan (Georgie), all of whom appeared in home movies dug up by Adult Sheldon.

Did you miss Cuoco’s cameo when it first aired? Or did you hear the voice of “Pool Water” and suspect that it belonged to the former resident of Apt. 4B? Watch (or rewatch) the scene above, then hit the comments with your reactions.