• 'The Big Bang Theory': Penny's mother and brother arrives for an awkward family reunion!

'The Big Bang Theory': Penny's mother and brother arrives for an awkward family reunion! (Photo : Getty Images/ Frederick M. Brown)

"Big Bang Theory" fans will finally meet Penny's mother and brother in the season 10 premiere. After nearly ten years of vague stories and questions about M.I.A family members, this is the "Big Bang Theory" moment fans have all been waiting for!

In a sneak peek obtained by ET, Kaley Cuoco reunites with her "8 Simple Rules" co-star and her former on-screen mom, Kaley Sagal, who is playing the role of her on-screen mother once again. Cuoco and Sagal stared daughter and mum in the ABC comedy from 2002-2005 for more than 75 episodes.

Like Us on Facebook

In addition to the "Big Bang Theory" arrivals, "30 Rock's" Jack McBrayer made his Big bang debut as Randal, Penny's brother who has been mentioned on the series as a drug-making criminal.

"The Big Bang Theory's" season 10 premiere is bringing everyone's families together to celebrate Penny and Leonard's wedding ceremony. Fans anticipates this season as Penny's last name might be revealed.

According to USA Today, guest list is rumored to dazzle at 'Big Bang Theory' wedding as a glittery guest list, including stars from Roseanne, Taxi, Cybill, Married ... with Children, 30 Rock and other past hits is expected. Such is common when TV's most-watched comedy throws a wedding.

In the clip, Penny and her dad, role played once again by Keith Carradine, are sharing a beer and talking about her career success as a pharmaceutical sales rep, while her mother chastises about Randall for not living up to his potential.

"Hey! She is just selling drugs, I had to make 'em," Randall proudly quipped.

McBrayer made a surprise appearance back in July at "The Big Bang Theory" panel at Comic-Con and made a joke that, unlike his character, he has only been to jail "recreationally," but he looks "real good in orange."

"The Big Bang Theory" Season 10 will premiere on Monday, Sept. 19 on CBS at 8 p.m. ET/PT.

Here is a video of how Star Kaley Cuoco defines "love":