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Actor Jim Parsons (crouching) poses with co-stars from the television series "The Big Bang Theory" (from L-R) Kunal Nayyar, Mayim Bialik, Melissa Rauch, Simon Helberg, Johnny Galecki and Kaley Cuoco-Sweeting, on his star after it was unveiled on the Hollywood Walk of Fame in Los Angeles, California March 11, 2015. Reuters/Mario Anzuoni

It’s all about celebrations this week on “The Big Bang Theory,” as the upcoming episode centres on Sheldon’s (Jim Parsons) birthday party. The whole gang, which includes Penny (Kaley Cuoco), Leonard (Johnny Galecki) Bernadette (Melissa Rauch), Howard (Simon Helberg), Amy (Mayim Bialik) and Raj (Kunal Nayyar), is also set for a more meaningful bash as CBS’ highly successful comedy series hits its 200th episode, titled “The Celebration Experimentation.”

The Feb. 25 run is set to become one of the most memorable “The Big Bang Theory” episodes, especially with a cameo by original “Batman” star Adam West. Wil Wheaton, Sara Gilbert, John Ross Bowie and Christine Baranski have also signed up to return and join “The Big Bang Theory” cast members for the celebration.

Spoiler Alert! This article contains "The Big Bang Theory" Season 9 spoilers. Read only if you want to know more about it.

TV Guide reports that the gang gets on a festive mood as they celebrate Sheldon’s birthday. To make his big day even more special, his friends arrange for a special guest.

The official YouTube channel of “The Big Bang Theory” posted sneak peeks of the upcoming episode. One teaser says that if there’s one thing that Sheldon hates, it’s his birthday. Spoilers say that it’s because when he was a kid, Sheldon had his share of birthday party nightmares. Despite this, he seems to succumb to his friends’ desire to celebrate his big day with a bash. “You may celebrate my life by throwing a party with friends and a shower of admiration and love,” Sheldon says. “But then you owe me big time.”

Everyone who’s anyone joins in the biggest party year, including the original “Batman” star, Adam West. Sheldon is shell-shocked when he sees the 1960s action series lead, toasting to him and greeting him a happy birthday.

Source: YouTube/The Big Bang Theory

On his Instagram account, Parsons posted a photo of him and his copy of the script for the show’s season 9 episode 17. “The Big Bang Theory” star wrote, “Even 200th episodes get re-writes,” with the hash tag #thankyouforwatching.

 

Even 200th episodes get re-writes #bluepages #200episodeshowoldami?!? #thankyouforwatching

A photo posted by Jim Parsons (@therealjimparsons) on

Kevin Sussman (Stuart) and Stephen Hawking (Dr Stephen Hawking) also appears on the upcoming episode, which is directed by Mark Cendrowski, according to IMDb. Click here to watch more of the show’s preview videos. Find out what happens next on “The Big Bang Theory” Season 9, which airs on Thursdays on CBS in the U.S.