'Big-bang Theory' Year 1-1 finale to feature guest appearance

Jamie McCarthy Frazer Harrison & Theo Wargo for Getty Images

Jamie McCarthy Frazer Harrison & Theo Wargo for Getty Images

As of this writing, it's not clear what Hamill's role will be. The network has now released a list of the event's returning and new guest stars, which includes Mark Hamill.

Meanwhile, other cast members who have appeared on the show are returning as their characters. Jerry O'Connell is also in the episode playing Sheldon's older brother Georgie.

Laurie Metcalf, who plays Sheldon's mom, Mary, is returning, as is Courtney Henggeler, who previously played Sheldon's sister, Missy Cooper, all the way back in Season 1. Lauren Lapkus from Orange Is the New Black has a recurring guest role as of the April 19th episode and will appear in the finale, perhaps as a new love interest to the remaining single friend, Raj (Kunal Nayyar). She could portray Amy's mother, although that role - which consisted of a small number of lines, over a Skype chat - has already gone to another bit actress, Annie O'Donnell.

Don't miss when The Big Bang Theory wedding of the century airs this May on CBS.

Amy's father, though mentioned in the dialogue in at least one episode, has not appeared on the show. Brian Posehn has recurred as Bert Kibbler on the series, and Wil Wheaton has played himself multiple times, as well.