This Thursday's "The Big Bang Theory" will air its first ever Thanksgiving episode, which promises to be filled with in-laws, drama and big surprises.

In the all-new episode, titled "The Thanksgiving Decoupling," the gang will celebrate the turkey holiday at Mrs. Wolowitz's house. However, they will be served with more surprises than just Raj's cooking at dinner.

According to Hypable.com, the gang will be hit with a blast-from-the-past guest star that will toss a wrench in Penny and Leonard's happy holiday. Brian Thomas Smith will return as Zack, who reveals that he and his ex-girlfriend Penny were actually married. It's hard to say how Leonard will react, since Penny freaked out whenever the subject of marriage arose between the two of them.

The official summary for upcoming episode of "The Big Bang Theory" indicates that he and Penny will approach the issue with a united front and that Sheldon will have strong feelings about Thanksgiving.

"Sheldon protests when the gang drags him to Mrs. Wolowitz's house for Thanksgiving. Meanwhile, Penny and Leonard must deal with a mistake from her past," reports IMBD.

In addition, Casey Sander will reprise his role as Bernadette's strict dad, Mr. Rostenkowski in season 7, episode 9 who will stress the importance of beer at a traditional Thanksgiving dinner.

"The Big Bang Theory" S7E9, "The Thanksgiving Decoupling," will air on Thursday, Nov. 21 at 8:00 p.m. on CBS. But until then, check out a sneak peak video below.