A season 3 episode of Young Sheldon featured The Big Bang Theory's Kaley Cuoco. Last May, the actress officially bid her role as Penny in the CBS popular sitcom farewell as it ended with 12 seasons - becoming the longest-running multi-camera show ever. However, she recently came back to the world of the genius, but socially inept Sheldon - several laters before their grown-up characters met in Pasadena.

Created by the same minds behind The Big Bang Theory, Chuck Lorre and Molaro, Young Sheldon debuted in 2017 as a prequel spin-off to its parent series. Set in 1989, it features Sheldon's years as a high school student in Galveston, Texas, before he moved to Pasadena and became roommates with Leonard. The show offers fans a peek at the life the fan-favorite character often talked about with his friends as his parents, George Sr. and Mary; siblings, Georgie and Missy; as well as Meemaw factor in the show's story.

Related: Young Sheldon Sets Up Georgie's Big Bang Theory Story

In a recent interview with TVLine, Molaro confirmed that Cuoco was indeed in the December episode of Young Sheldon titled "Teenager Soup and a Little Ball of Fib." In the outing, Sheldon dreams about speaking to the pool water in light of the impending swim test which he's dreading. Cuoco was uncredited for the role, but now the executive is making this fun detail known.

“That was absolutely the voice of Kaley as pool water. 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.'”

“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?' She just laughed and said, ‘Absolutely, I do.'”

Big Bang Theory Penny and Sheldon

When asked why they opted against promoting the fact that Cuoco is coming back to The Big Bang Theory world even just for a voice cameo, Molaro explained that they wanted it to be a surprise. And since the actress' involvement was uncredited for months now, they wanted it to be some kind of treat for those loyal viewers who picked up on it. In hindsight, it's an interesting take considering that putting the information out there before the episode aired would've enticed more viewers to watch the series - especially fans who still misses Penny and the original show.

“Sometimes I feel a little weird about things being over-promoted. 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.”

Given the time-frame, there wasn't much narrative connection between the shows aside from having some similar characters. Although, CBS did try to link them better together last year as they positioned the prequel spinoff as their next big sitcom with its parent show wrapping up. Aside from the unconventional crossover that saw George Sr. and Georgie appear through an old videotape in one of the final episodes of The Big Bang Theory, Young Sheldon paid homage to its predecessor by also revealing young versions of Sheldon's future friends in their season 2 finale. .

More: What Happened In The Big Bang Theory’s Original Pilot (& Why It Was Changed)

Source: TVLine