Spoilers for the latest episode of Young Sheldon – “Graduation” – lie ahead.

Young Sheldon kicked off its fourth season with a sweet commencement-centric episode that saw the titular child prodigy graduate from high school. And in the closing moments of the episode, fans of The Big Bang Theory were treated to a surprise vocal cameo from fan-favorite character Amy Farrah Fowler, who was played by the returning Mayim Bialik.

The episode ends with a graduation party for Sheldon and his sister, Missy. The older Sheldon who narrates the show mentions that it was the best graduation party he’d ever been to, until the one held for his son, Leonard Cooper. He then mentions that he wanted to name his son Leonard Nimoy Cooper, before Amy cuts in and says that he should just be glad she let him their son Leonard.

The cameo came as quite a surprise for fans of the show, but it was definitely a welcome one. As perfect as the moment was, series co-creator Steve Molaro revealed that Amy’s role wasn’t initially part of the script:

[Amy’s voiceover] was not in the script yet [pre-pandemic], but Sheldon talking about his son, Leonard Cooper, always was.

The Big Bang Theory and Young Sheldon producer went onto explain to TVLine that the idea stemmed from his desire to add in the Leonard Cooper joke, which he had been pondering for a while. He then got the idea to add in a rebuttal from Amy and called up Mayim Bialik to see if she would be interested:

Going through the script again, I wanted to add in a joke that I had been thinking about for a long time: that Sheldon might want to name his son Leonard, and give him the middle name Nimoy. Then I was toying with [the idea], ‘Wouldn’t it be nice to hear Amy say, ‘“Just be glad I let you name him Leonard’’?’ And I thought, ‘Well, there’s no rules on narration. Let’s put it in and see if Mayim will do it.’ I gave Mayim a call and she was happy to [do it]; [she] thought it was really fun.

Mayim Bialik actually isn’t the first Big Bang Theory alum to make a vocal cameo on Young Sheldon. Kaley Cuoco, who played Penny on the parent show, lent her voice to a pool monster that appeared in one of Sheldon’s nightmares. So far, the producers are finding some interesting ways to utilize legacy actors for the spinoff.

Since Molaro and his team don’t seem to be beholden to any strict rules when it comes to narration, there’s a good chance this won’t be the last time we get a cameo like this. We could hear other characters pop in to give their two cents on Sheldon’s narration before the series ends. I wouldn’t mind hearing Leonard or Raj jumping in to question something Sheldon has said.

New episodes of Young Sheldon air Thursdays at 8 p.m. ET on CBS, and past seasons are available to stream on HBO Max.

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