Plans for a renewal hadn't been discussed following season 12. However, most of the cast assumed there was at least one more season in the works. Jim Parsons had different plans, content with his work and aiming to end his deal during season 12. This meant The Big Bang Theory was coming to an end, and plans needed to be made in order to properly wrap the show up.

The finale received a lot of praise, given that there wasn't a sense of closure. A major highlight of the episode also features Sheldon giving his Nobel Prize speech. We'll take a look back at that scene, while showcasing Parsons' reaction to Sarah Michelle Gellar taking part.

The actress appearing on the episode was a major score for Chuck Lorre and the series. However, as it turns out, the actress didn't need much convincing. We'll reveal what the negotiation process was like, and how her cameo was handled behind the scenes.

Sarah Michelle Gellar Instantly Agreed To Appear On The Big Bang Theory Given That Her Family Loved The Show

How did Sarah Michelle Gellar's cameo come about? Well, it helps that those in the writers' room were big fans of Buffy The Vampire Slayer.

In addition, Chuck Lorre saw an opening for a celeb to appear alongside Raj in the finale, and took full advantage of it.

Speaking alongside Yahoo Entertainment, showrunner Steve Holland revealed it didn't take much to convince Sarah Michelle Gellar given that her family loved the show.

"Well, Chuck spoke to her, but it's always a good sign when the first thing people say is, "Our family are huge fans of this show!" That was how it went with Sean Astin too. We reached out and he's like, "Our family are gigantic fans, we watch every week!" So then it's like you're pretty safe and then it was just a matter of working out scheduling with Sarah.

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It turned out to be a memorable cameo and one that surprised lots of fans, especially given that the sitcom was able to keep it a secret. It also caught the cast by surprise, including Jim Parsons.

Showrunner Steve Molaro Revealed Jim Parsons Was Genuinely Surprised By Sarah Michelle Gellar's Appearance

The Big Bang Theory finale sees Sheldon claim his Nobel Prize. More importantly, Sheldon gives an emotional speech, thanking his close friends for their contributions. There is some added lightness to the moment, particularly when Sheldon sees Sarah Michelle Gellar in the audience next to Raj.

According to Steve Molaro, Sheldon's reaction was completely genuine.

"That was a genuinely stunned and confused look on his face as he said, "Is that Buffy the vampire slayer?" in the middle of his Nobel speech. It was so great."

There was another element the showrunners wanted to ensure during her cameo, and that was the fact that she was not on a date with Raj. The writers wanted to honor her real-life relationship with Freddie Prinze Jr. in doing so.

"It seemed funny. We know in real life she's married to Freddie Prinze Jr. and, obviously, it's a TV show, but it was just a funny way to cover our bases and get a joke in and give her a good laugh along the way.

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An entertaining moment and a cameo fans really enjoyed.

Jim Parsons Thought The Big Bang Theory Wrapped Up In The Right Way

Getting to the finale was a difficult process for the cast. When Jim Parsons revealed he wasn't returning for season 13, it meant the end of the show. Kaley Cuoco instantly wept, while it took the cast a moment to understand the magnitude of such a decision.

The final table read was a hard one, with the cast completely emotional over their final lines. Sheldon in particular had some touching moments, especially during his speech.

The actor admitted there was a lot of pressure to get the finale right, and for the most part, comedies don't succeed in doing so. However, the actor mentioned that the show did the best job possible.

"It ended in the way that I hoped it would, in that it felt right. There were probably a million different ways it could feel right," Parsons tells Digital Spy.

"I would talk with some of the writers and I know as they were writing it they were nervous," he added. "I said, 'It's the finale, you can't get it completely right. Someone's gonna hate it. But I don't think that was actually the case with this, which was really sweet. I think it wrapped up in the right way."

Lots of fans agreed that the show ended the perfect way, without a sense of closure. All fans needed to know was that everything was going to be okay, while the friends continued on with their lives.