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Bazinga! 'Young Sheldon' reveals the origin of 'Big Bang Theory' catchphrase

This is how it all began!
/ Source: TODAY

For years, fans of "The Big Bang Theory" have wondered exactly where Sheldon's catchphrase "bazinga!" came from.

And after all this time, we found out on Thursday, on "Young Sheldon"!

Sheldon (Iain Armitage) decided to bring out his funny bone on "Young Sheldon," with long-lasting results. CBS

The youthful boy Sheldon on "Sheldon," played by Iain Armitage, worried that being so serious would lead to him becoming a poorly-adjusted grown-up. (There's a joke in that assumption in the first place, since we already know just how well grown-up Sheldon, played by Jim Parsons, fits in.)

So in order to try and be fun-loving and goofy like all the other kids, Sheldon headed down to the comic book store and bought practical jokes off the shelf ... made by a company called the Bazinga Novelty Company.

Catch phrase, "If it's funny, it's a Bazinga!"

And so, Sheldon went about bazinga-ing everyone, from dad (fake stick of gum) to his sister (whoopee cushion) though he failed to surprise his brother (can of snakes) ... and tricking Meemaw went a little awry when his prank phone call had to be left on an answering machine.

Every time he pulled off a successful pank, Sheldon cried out, "bazinga!"

Armitage apparently totally fell for the prop sign, and now has it close to his heart:

One fan even had an alternate theory of where the word came from, which has a terrific scientific angle:

"And that's how I became the madcap prankster all my friends know and love," Parsons, as adult Sheldon, narrated on the show.

That's kind of the biggest prank of all, when you think about it!