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(CNN) —  

The following contains spoilers about “The Big Bang Theory” series finale.

“The Big Bang Theory” finale showed off the program’s big heart, celebrating the friendship — quirky as it was — that has been the backbone of the CBS sitcom over 12 seasons.

In that respect, the one-hour finish felt satisfying and appropriate, if somewhat low-key, eschewing huge fireworks that which would have likely felt like something of an overreach, to simply echo what has made the show so popular over the course of its run.

The central plot, teased out over multiple episodes, culminated in Sheldon (Jim Parsons) and Amy (Mayim Bialik) winning the Nobel Prize in physics, offering the gang a chance to go on a trip to commemorate their triumphant moment.

What it was like at the final taping of ‘The Big Bang Theory’

As it turned out, though, the episode (rather sweetly credited to a dozen writers, including co-creators Chuck Lorre and Bill Prady) served as a conduit to showcase the way in which the show itself has changed — adding key female characters, marrying off the guys and graduating to more grown-up problems and issues, without giving up their passion for things like comic books and “Star Wars” movies.

The graduation to adulthood saw the characters take another major step in the finale, as Leonard (Johnny Galecki) and Penny (Kaley Cuoco) learned that they were pregnant — joining Howard (Simon Helberg) and Bernadette (Melissa Rauch) in the parents club — a revelation the self-absorbed Sheldon treated with complete indifference.

Young Sheldon’ paid sweet tribute to ‘The Big Bang Theory’

The evolution of Sheldon has been the most fascinating aspect of the show, and at times the most challenging. Brilliantly played by Parsons, the character is, above all else, a creature of habit and routine, which made his deer-in-the-headlights response to the Nobel ring true. “All this change is just too much,” he griped to Penny, in one of their shared moments that have frequently provided series highlights.

Being a “selfish jerk,” as Leonard called him, has always been part of Sheldon’s charm — or at least, what has made the character so oddly endearing. Still, Sheldon’s closing tribute to his friends reflected how, in his unorthodox manner, he obviously cherished them, in the same way he overcame his selfishness to enter into a relationship with Amy that nobody could have possibly envisioned when the series began.

The show did indulge in one bit of guest casting, tossing in “Buffy the Vampire Slayer’s” Sarah Michelle Gellar, and worked in a few of the supporting players. But the spotlight remained steadfastly and wisely trained on the core cast.

Lorre’s vanity card closed with two simple words, “The End,” and the final shot showed the seven stars sitting around on a couch, as viewers have seen them do so often before.

Of course, it’s not really the end, with “Young Sheldon,” the spinoff prequel, carrying the banner and championing the cause of lovable science nerds. Nevertheless, in terms of the tricky math that goes into calculating a proper sendoff, “The Big Bang Theory” seemed to get the formula just about right.