The Big Bang Theory season 9
Penny and Beverly in The Big Bang Theory season 9CBS

CBS will air The Big Bang Theory season 9 finale this Thursday (12 May) at 8pm EST, where Sheldon Cooper's mother Mary and Leonard Hofstadter's recently divorced parents Beverly and Alfred will guest star.

This is the first time since the show' premiere that fans will meet Leonard's father (played by Judd Hirsch). Episode 24 is titled The Convergence-Convergence and the official synopsis reads as follows:

In the previous episode, Penny struggled to make an honest connection with her mother-in-law Beverly, who was in town to visit them. After Penny's insistence, she revealed that she was not happy with that fact that Penny and Leonard didn't invite her to their wedding. The episode ended with Penny offering to have a second wedding with friends and family, thereby setting up the finale episode.

A promo released by CBS for the finale episode shows Mary Cooper, Sheldon, Amy, Penny and Beverly sitting in their apartment awkwardly, as Sheldon declares: " Oh isn't this nice!" The promo voice-over says: " Everyone's excited about the biggest season finale of the year. And for the first time ever meet Leonard's dad Alfred. "

After Alfred makes a snippy comment at his recently-divorced wife saying: "Hello my hateful shrew!" Beverly immediately hits back: " How are you! You wrinkled old b*****d." This makes the family reunion more awkward, even as Sheldon points out: " Alright! Now I am starting to sense a little tension."

Warning: Spoilers ahead

According to a leaked report, Leonard's father and Sheldon's mother will find something in common, aka their hatred for Beverly. Meanwhile, Penny and Leonard will decide to redo their wedding and they will even plan a family dinner. But chaos ensues when Beverly and Mary don't get along and Alfred takes a sudden interest in Sheldon's mother.

The report also suggest some kind of a hook-up between the two. The episode will end with Sheldon trying to call his mother and Leonard texting Alfred but neither will respond. Penny suggests that they might have turned their phones off, even as Sheldon and Leonard get disturbed by the revelation that there might be something going on between their parents.