Happy Birthday, Sheldon! Big Bang Theory is ready to go all out for the scientist's big day, and fan can catch the series 200th episode online.

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Sheldon (Jim Parsons) has never let the gang throw him a birthday bash, but during "The Celebration Experimentation," Leonard (Johnny Galecki) and Co. will pull out all the stops to make sure their quirky pal has a party he'll never forget.

The series' milestone episode will see appearances from sci-fi legends Wil Wheaton and the original Batman, Adam West!

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"We'd been trying to get him for a while," showrunner Steve Molaro said of the Dark Knight's highly anticipated appearance, according to TV Guide. "We tried last season and came pretty close. We were super excited to get him this year; it's always tricky when actors are playing themselves. But he was incredibly nice and deeply funny."

Fans can catch Sheldon, Leonard, Penny (Kaley Cuoco), Raj (Kunal Nayyar), Howard (Simon Helberg), Amy (Mayim Bialik), and Bernadette (Melissa Rauch) at 8 p.m. ET on CBS. The episode will be online here starting at 1 a.m. ET/10 p.m. PT.

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