Throughout its 12 season and 12 year run, Chuck Lorre's blockbuster CBS sitcom "The Big Bang Theory" played host to a ton of guest stars, from several "Star Trek" veterans to the late James Earl Jones and the legendary scholar Stephen Hawking. According to an oral history of the series, though, one particular Oscar winner, Sandra Bullock, had to turn down a role in the series finale, "The Stockholm Syndrome," due to scheduling conflicts.

In Jessica Radloff's 2022 book "The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series," executive producer Steve Holland revealed that the show's creatives tried to book Bullock for a short cameo opposite Kunal Nayyar's character Raj Koothrappali in the episode, but she wasn't available, so "Buffy the Vampire Slayer" star Sarah Michelle Gellar stepped in. So, what was the scene in question? While Sheldon Cooper (Jim Parsons) and his wife Amy Farrah Fowler (Mayim Bialik) accept their Nobel Prize in physics for their work in super asymmetry, their friends Leonard and Penny Hofstadter (Johnny Galecki and Kaley Cuoco), Howard Wolowitz and Bernadette Rostenkowski-Wolowitz (Simon Helberg and Melissa Rauch), and Raj watch from the audience. Raj is inexplicably joined by Gellar, who tells him they are not on a date.

"Sandra Bullock was actually our first go-to because of Koothrappali's long love of her," Holland said in the book. "We were really excited about it, but we got a polite decline because she was shooting a movie and wasn't available. But we were very excited Sarah was available to come on. And we had mentioned 'Buffy' before in the series, where Leonard was going to show 'Buffy' to Penny. We were also big 'Buffy' fans in the writers room, so it really worked out well."