"The Big Bang Theory" fans are going to meet Penny's (Kaley Cuoco) family when the 10th season premieres on Sept. 19. Her father has already been introduced, but viewers are going to get acquainted with her mother and brother when they arrive for her wedding.

Katey Sagal will be playing Penny's "neurotic" mother, while Jack McBrayer of "30 Rock" fame will be portraying her brother, who is also a drug dealer.

"This is her first time meeting Leonard's parents and friends and she wants to make a really good first impression. How she and her family come off to these people is extremely important to her," executive producer Steve Molaro told TVLine.

As fans know, Penny's side of the family has always been an enigma, although she has brought them up on a few occasions. It will certainly be interesting to see how their family dynamic will play into things, especially considering the possibility that Leonard's (Johnny Galecki) father and Sheldon's (Jim Parsons) mother really slept together in the season 9 finale.

However, Sagal and McBrayer aren't the only ones set to guest star in the upcoming season. Molaro also revealed that Brandon Jones will be appearing in an episode as The Flash, whom fans will see in a dream of Sheldon's. "It's a Flash we may not be used to," he teased.

Apart from that, Molaro also revealed that Sheldon will take his relationship with Amy (Mayim Bialik) one step further by toying with the idea of moving in together.

"It will be viewed very clearly as an experiment, because the easiest way to get Sheldon on board with the idea is to disguise it as a [situation] where he's collecting data, and something he can ultimately reconsider in the name of science," Molaro explained.

As for the rest of the group, Howard (Simon Helberg) is getting ready to be a father as Bernadette (Melissa Rauch) was revealed to be pregnant last season. Molaro explained that she will have some conflicting feelings about her situation since she made it clear before that she does not want children.

As previously reported, the premiere episode picks up a day after the season 9 finale. Beverly (Christine Baranski) will consider leaving before the wedding even takes place because of recent events, but she ends up staying.