In its 12 seasons, The Big Bang Theory didn't often start with "previously on" openings, but in the series finale of the CBS show, which aired Thursday night, it started with possibly the longest "previously on" in TV history. It walked the audience through clips from the past 11 years: Penny (Kaley Cuoco) meeting her new neighbors, Leonard (Johnny Galecki) and Sheldon (Jim Parsons); Penny and Leonard falling in love; Sheldon knocking on countless doors (three times, of course); "Soft Kitty"; everyone falling in love; three weddings and two babies. It was a bittersweet walk down memory lane as the show began its final hour.

The second-to-last episode begins where it all started: in Leonard and Penny's (formerly Leonard and Sheldon's) apartment. The couple is trying to stay awake while Amy (Mayim Bialik) and Sheldon wait for a call to learn if they have won the Nobel Prize. After a prank call from Kripke, Amy gets the call: They've won the Nobel Prize in Physics.

The next day both Amy and Sheldon are elated with their accomplishment. They get texts from friends and family praising them for winning the medal. Amy says their lives will never be the same — and that's right when they're bombarded by press outside the apartment building. Sheldon sneaks back inside. He does the same later at the CalTech cafeteria, where he and Amy get a standing ovation. He even hides under his desk when a reporter tries to interview him.

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Meanwhile, Raj (Kunal Nayyar) hears Amy crying in the women's restroom. She's seen her picture all over the internet and she hates how she looks. Raj jumps at the chance to help her spend her Nobel Prize winnings on a makeover. He was made for this moment.

Back at the apartment, Sheldon tells Leonard he's struggling with all the attention. And that's when Raj walks in with his new project: Dr. Amy Farrah Fowler with a short, curly 'do and a sleek new wardrobe. Sheldon storms out, saying he preferred the old Amy. Outside the apartment door, he tells Leonard that Amy was his one constant and he's not liking all the change when THE ELEVATOR DOOR OPENS. Inside, Penny says, "Can you believe it? They finally fixed the elevator!"

<em>The Big Bang Theory</em>The Big Bang Theory

Sheldon says it's a nightmare and runs down the stairs to find Penny waiting for him (not only is the elevator fixed after all these years, but it's fast). She offers him a ride to the Cheesecake Factory — which, throwback alert, they haven't been to in quite a few seasons. The two talk about how much has changed since they first met each other, and Sheldon comes to realize that change isn't necessarily bad.

Then they see Howard (Simon Helberg) and Bernadette (Melissa Rauch) on the TV talking to CNN about their "best friends" the Nobel Prize Laureates. Sheldon decides to have a drink (90 percent Hawaiian punch, 10 percent vodka) with Penny.

They must have had a few drinks because the next episode begins with a two-month fast-forward in which we learn Penny and Leonard conceived later that night. As everyone readies to fly to Sweden for the Nobel Prize ceremony, the expecting parents are keeping their news quiet.

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But on the flight there, Sheldon worries that Penny has a stomach bug and will get him sick, causing him to miss his big day. He confronts Leonard about it, so his former roommate tells him the good news. Sheldon's response is basically a non-response. Amy is thrilled though — she thinks that she and Penny are "sister wives" when she hears she got pregnant after a night of drinking with Sheldon. (They're not.)

Once everyone gets settled into the hotel, Bernie and Howard FaceTime with Stewart to find out that his babysitting isn't going so well. Michael has a fever and Halley lost a tooth when she fell down the stairs. They go to tell Sheldon they're going to head home, and without any empathy for their situation, Sheldon gets upset. Already furious that Sheldon didn't get excited for his upcoming child, Leonard says they're leaving, too.

<em>The Big Bang Theory</em>The Big Bang Theory

As they prep for their big night, which they'll now be at alone, Sheldon tells Amy he doesn't understand why all his friends are being selfish. She tells him that he broke all their hearts, and he says that's not what he meant to do. She tells her husband she knows he didn't mean to, which is the only reason people tolerate him. "Does that include you?" Sheldon asks. "Sometimes, yeah," Amy says.

Sheldon is finally realizing his dreams, being medaled with the Nobel Prize in Physics, and yet he's upset about what happened earlier that night. He isn't enjoying his moment. That is, until he hears his friends cheering for him from the second row. They're all there, including Buffy, the vampire slayer (the show's final special guest, Sarah Michelle Gellar), who sat next to Raj on the flight and somehow got conned into attending with them.

Amy gives a call to all young girls interested in pursuing a career in science to follow their dreams, and then she hands over the mic to her husband. He puts aside the 90-minute long speech he prepared, which he admits was mostly self-centered. He says the honor of this award doesn't just belong to him. He shouts out to his family and his "other family." He acknowledges that he couldn't have done this without them.

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"I've been encouraged, sustained, and tolerated not only by my wife, but by the greatest group of friends anyone ever had," Sheldon says. They he asks them to stand and calls them out one by one, even acknowledging "astronaut Howard Wolowitz." He then says that he knows Leonard and Penny will have smart and beautiful babies. And he apologizes for not being the friend they deserve, but in his way, he loves them all.

It's a tearful, sweet moment to end the series. No, Raj didn't get married. No, we didn't ever learn Penny's last name. And there was only one pregnancy (fans were hoping to see Amy pregnant since her and Sheldon's children were foretold on Young Sheldon). But this was a fitting way for the show to end. The Big Bang Theory was always about the friendships — originally the four guys, and growing beyond that as they grew — and that's why this ending worked so well. And, hey, we got a fixed elevator and to see both of Bernie and Howard's kids! All in all, it was a successful, fan-wish-filled finale.

And there's one last moment: Before the credits roll, the cast sits on the couch and eats Chinese food while an acoustic version of the theme song plays them out. It must be Friday night.

(Disclosure: TV Guide is owned by CBS Interactive, a division of CBS Corporation.)

<em>The Big Bang Theory</em>The Big Bang Theory