'The Big Bang Theory': Sheldon Takes a Huge Step Forward in the 200th Episode!

WARNING: We're about to reveal what happened in tonight's 200th episode of The Big Bang Theory. If you do not wish to join in on the festivities, leave now. For everyone else, grab a gift and let's party!

After nine years, 200 episodes, and countless storylines later, The Big Bang Theory has finally given us something brand new to celebrate: Sheldon Cooper's birthday!

During Thursday night's landmark episode, Big Bang answered a question that many fans have always wondered about: why doesn't Sheldon like to celebrate his birthday?

WATCH: Kaley Cuoco Talks 200th Episode of 'Big Bang Theory'

In a heartbreaking reveal, Sheldon explained that every year on his birthday, his twin sister's friends would torture and humiliate him. "When I was six, they told me Batman was coming to my party," Sheldon confessed to Leonard, Penny and Amy. "I waited by the door for hours. The closest thing to Batman that I saw was when a Robin flew into the window."

When Amy expressed her deep desire to throw Sheldon the ultimate birthday party, he was naturally cautious to relive those buried memories, but she eventually won him over.. "You made my last birthday so memorable I wanted to return the favor," Amy said, referring to their big sleepover earlier this season.

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To celebrate the big occasion, CBS brought back many special guests who have played some of the most beloved characters in the Big Bang universe, including Christine Baranski as Beverly Hofstadter, Sara Gilbert's Leslie Winkle, and Wil Wheaton as his wonderfully sarcastic self.

Not only did our favorite group of beauties and geeks throw Sheldon the perfect birthday bash, they even surprised him with an extra special gift: Batman! That's right, the one and only Adam West was invited to the nerd-tastic event, thus fulfilling Sheldon's long overdue birthday wish.

The Big Bang Theory airs Thursdays at 8 p.m. ET/PT on CBS.

Press play on our video below to get the behind-the-scenes scoop from The Big Bang Theory cast at the 200th episode celebration!