The Adorable Cameo Young Sheldon's Iain Armitage Made In The Big Bang Theory

When Season 12 of Chuck Lorre's "The Big Bang Theory" premiered in 2018, it was a bittersweet time for audiences. In just a few months, the story of Sheldon Cooper (Jim Parsons), Leonard Hofstadter (Johnny Galecki), Penny (Kaley Cuoco), and the rest of these beloved characters would come to an end. Well, almost.

At the same time, "Young Sheldon" was celebrating the premiere of its second season on CBS, allowing fans to still enjoy their favorite theoretical physicist, but during his childhood years. Starring Iain Armitage as the highly intellectual, bowtie-wearing Sheldon, the sitcom chronicles his upbringing in Galveston, Texas. "Young Sheldon" Season 1 was largely well-received. On Rotten Tomatoes, it garnered 76 percent on the Tomatometer and 75 percent for the audience score. Kevin Fallon of The Daily Beast commented, "With 'Young Sheldon,' Lorre's wielding a sledgehammer with reckless abandon. And, in fixing it, he is producing perhaps his most inspired work in years."

This new creation by Lorre wouldn't be possible without Parsons, who had brainstormed a series based on his nephew, a very smart kid who didn't exactly fit in with his family. Because it felt too similar to Sheldon's upbringing, Parsons presented the idea to Lorre, who loved it. Naturally, Parsons is heavily involved with "Young Sheldon" as an executive producer and, much to fans' delight, the narrator of many episodes.

It's widely known that Parsons is a huge part of "Young Sheldon." But some fans might not remember that Armitage has an adorable appearance on "The Big Bang Theory."

Iain Armitage gives adult Sheldon a pep talk in Season 12

In "The Big Bang Theory" Season 12, Episode 10 ("The VCR Illumination"), Sheldon isn't in a good headspace upon learning that his and Amy Farrah Fowler's (Mayim Bialik) theory on super-asymmetry had already been tackled. Sheldon then begins to reevaluate every opinion he's ever had. To assist, Leonard pulls out a videotape that Sheldon told him to safeguard unless it's an emergency. The tape features a pep talk recorded by his younger self, portrayed by Armitage, to someday help his future self. After all, the only person Sheldon takes advice from is, well, himself.

This isn't the only "Young Sheldon" star to appear. The pep talk is cut off by a high school football game, accidentally recorded by Sheldon's father, coach George Cooper Sr. (Lance Barber). Surprisingly, the speech given by George in the locker room ("You learn as much about who you are and what you're made of from failing as you do from success") deeply resonates with Sheldon. It's quite the tear-inducing scene since, as fans know, George passes away when Sheldon is 14.

Executive producer Steve Holland said of the episode (via USA Today), "[It] was a big one and checks a big box off. We wanted to find a fun way to connect these two shows."

Off-camera, the two Sheldons boast a similar dynamic. Just as young Sheldon attempts to rehabilitate adult Sheldon's passion for science, Armitage rehabilitates Parsons' love of acting. He said of Armitage in an interview with ET, "There's just a way in which he's tackling all of this that is such fun and such joy of the process. You're a reminder to, I think, anybody who's been doing it a while to remember how much fun it is."