One of NBC's brand new fall series has added another key cast member in advance of its fall debut. According to The Hollywood Reporter, Clifton Collins Jr. has joined the cast of the upcoming drama series The Event.

Collins Jr. will portray Thomas, and it was said that he will play a large part in the show's conspiracy, with his character on a conflicting side against the President of the United States, who is being played by Blair Underwood.

We announced just yesterday that NBC has set a premiere date of Monday, September 20 for the show, which will air at 9 PM ET. We also announced last month that NBC will be screening the entire pilot of The Event at this year's Comic-Con in San Diego, with the screening taking place on Saturday, July 24 at 11:15 AM in Room 6A of the San Diego Convention Center. You can find a rundown of the full cast and synopsis below.

The Event is an emotional high-octane conspiracy thriller that follows Sean Walker (Jason Ritter, The Class), an Everyman who investigates the mysterious disappearance of his fiancée, Leila (Sarah Roemer, Disturbia), and unwittingly begins to expose the biggest cover-up in U.S. history. Sean's quest will send ripples through the lives of an eclectic band of strangers, including: newly elected U.S. President Martinez (Blair Underwood, Dirty Sexy Money); Sophia (Emmy Award nominee Laura Innes, ER), who is the leader of a mysterious group of detainees; and Sean's shadowy father-in-law (Scott Patterson, Gilmore Girls). Their futures are on a collision course in a global conspiracy that could ultimately change the fate of mankind. Ian Anthony Dale (Daybreak) and Emmy winner Zeljko Ivanek (Damages) also star in the ensemble drama. The Event is a production of Universal Media Studios and Steve Stark Productions. Stark (Medium, Facing Kate) serves as executive producer, Nick Wauters (The 4400, Eureka) is creator/co-executive producer and Jeffrey Reiner (Friday Night Lights, Trauma) is the director/executive producer.; Evan Katz (24) also is an executive producer.