Note: The following article contains spoilers.

The Big Bang Theory has signed off with a bittersweet series finale that many fans have called a "perfect" goodbye to the sitcom.

Twelve seasons of Bazingas came to a close on Thursday night (May 16) with a two-part series finale that offered a hopeful glimpse of where Sheldon, Amy, Leonard and Penny's lives would go off-screen in the future.

Last season ended with Amy and Sheldon's wedding , and Thursday's two-parter 'The Change Constant'/'The Stockholm Syndrome' opened with two more major milestones: the couple found out they'd won the Nobel Prize... and someone finally fixed the elevator!

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Improved elevator access aside, cracks started to show for Amy and Sheldon pretty quickly after their Nobel win when they were thrust into the limelight.

Sheldon's social anxiety took hold once again, whereas Amy started feeling insecure about the world judging her appearance. With some help from Raj, she got a whole new look – but Sheldon was none too pleased.

"I like you better the way you were," he snapped at his wife.

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While Penny took Sheldon for a drink to convince him "change" didn't have to be so scary, Amy, Leonard and Raj were back at the apartment ranting about how they were done putting up with his antics.

Penny seemingly managed to talk some sense into Sheldon, and even got him to introduce some "change" into his routine by riding the elevator back up to the apartment.

All of the Amy and Sheldon drama was keeping everyone so busy that Leonard and Penny were able to temporarily keep some big news of their own secret: they're expecting a baby!

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Penny's pregnant, sheldon and Amy got the Nobel prize, the elevator works this series finale has it all #BigBangTheory @bigbangtheory pic.twitter.com/jvtDFmVKTU — 💙🦂Scorpiogirl2🦂💙 (@NellyBelle3379) May 17, 2019

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The happy news came out when a paranoid Sheldon became consumed with the fear that Penny had caught a stomach bug on their flight to Sweden for the Nobel gala.

Leonard and Penny anxiously decided to let their friend in on their big secret, telling him Penny was pregnant rather than sick!

"You're right, I can't catch that," a nonplussed Sheldon quipped, before returning to his seat and telling his wife: "Good news Amy, she's just pregnant."

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Sheldon's insensitive reaction drove a further wedge between himself and Leonard, who told off his friend for ruining such an important life milestone.

"You are a selfish jerk. To hell with you and your Nobel Prize," Leonard yelled.

Sheldon's behaviour was so alienating that Penny, Leonard, Howard and Bernadette all threatened to leave the trip to Sweden early to head back to Pasadena.

It was time for Amy to step in and lay it all on the line for her husband.

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"They're abandoning us because you broke their hearts," Amy told him. "You never mean to. It's the only reason people tolerate you."

"Does that include you?" a heartbroken Sheldon asked, with Amy admitting: "Sometimes, yes."

Her honesty seemed to finally resonate with Sheldon. When it came time for the Nobel ceremony, he chose to set aside his "self-centred speech" to pay tribute to Penny, Leonard, Howard, Bernadette, Raj and Raj's date Buffy the Vampire Slayer (yes, actual Sarah Michelle Gellar had a cameo) after spotting them in the crowd.

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"I was under the misapprehension that my accomplishments were mine alone," he told the Nobel crowd.

"Nothing could be further from the truth. I have been encouraged, sustained, inspired and tolerated not only by my wife, but by the greatest group of friends anyone has ever had."

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After asking each of them to stand for recognition, Sheldon ended with a special mention to his "two dearest friends in the world" Penny and Leonard.

"I was there the moment Penny and Leonard met," he recalled. "He said to me that their babies would be smart and beautiful. And now that they're expecting, I have no doubt that will be the case."

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Friends like these come once in a lifetime. ❤️ pic.twitter.com/IgoOYNRdqx — The Big Bang Theory (@bigbangtheory) May 17, 2019

Sheldon finally having a moment of self-reflection was a "perfect" way to end the series for many diehard fans:

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Incredible final episode! I laughed, I cried and will miss this show! #BigBangTheory pic.twitter.com/gQ10GFcls5 — World Traveler! (@hockeync225) May 17, 2019

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@bigbangtheory season finale was so damn good. I'm not ready for it to be over. Thanks for the bazillion laughs, fantastic writing and one-of-a-kind characters. This show means so much to me for so many different reasons 😭😭😭#BigBangTheory #BigbangFinale pic.twitter.com/pTsCFX307d — Mally K (@mallyk13) May 17, 2019

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Thank you #BigBangTheory for 12 great years 😭. Perfect way for a show to end ❤️ — sam-jam 🎃 (@SammiBiebs) May 17, 2019

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That was perfect. Laughter, tears, etc. Amy and Sheldons speeches gave me all the feels. #BigBangTheory — Elizabeth Beauregard (@ElizabethBeaur9) May 17, 2019

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Thank you for ending this show the way it was ment to be it was truly amazing❤😥 #BigBangTheory — Amanda Roberts (@abrowncb528) May 17, 2019

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Now that was a perfect ending #BigBangTheory — Jessie (@tweetsbyjessie) May 17, 2019

And as we say goodbye, let's celebrate the elevator finally getting fixed!

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Loving every single thing about the #BigBangTheory series finale.



Elevator works pic.twitter.com/8C2afjdHrD — Tomi @3Boys_OldLady (@3Boys_OldLady) May 17, 2019

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Nobel Prize winning tenants = fixed elevator! #BigBangTheory — Bill Donovan (@PurdueBill00) May 17, 2019

In case anyone missed it, the trademark end-card from creator Chuck Lorre was appropriately understated for this last episode. It simply read: "The end."

Viewers didn't actually have to wait long to see more of their favourite Big Bang Theory characters. Directly following Thursday's series-ender was the season finale of prequel Young Sheldon.

That episode featured the young versions of Leonard, Penny, Howard, Raj, Amy and Bernadette in a sweet tribute to Big Bang Theory – and there may even be more chances to see their miniature versions since Young Sheldon has been renewed for two more seasons.

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"It was always my dream to win the Nobel Prize. I bet Sheldon will." #YoungSheldon pic.twitter.com/PkPfe6CkWB — Young Sheldon (@YoungSheldon) May 17, 2019

While fans are undoubtedly sad to see Big Bang Theory ending, series star Jim Parsons offered a sensible explanation this week for why he turned down making another season.

"There was no factor; there was no situation that I was like, 'Well, I've had enough of that.' No," he explained. "There was nothing like that. It was just... when you know, you know.

"And you're susceptible and thrown around by the whims of your own existence and getting to a certain age and your life changes and suddenly you just think different."

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However, fans shouldn't totally give up hope of seeing these characters again since Kaley Cuoco has said she would sign up for a Penny spin-off if Lorre ever asked.

The Big Bang Theory's final season airs on Thursdays at 8/7c on CBS and CBS All Access in the US. E4 airs the show in the UK.

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