'Chuck' Season 5: 'Smallville's' Justin Hartley and 'Lost's' Jeff Fahey to guest star as brothers

"Chuck" has always been a magnet for guest stars with serious geek cred, and its fifth and final season is certainly no exception. "Smallville" actor Justin Hartley tweeted on Tuesday that he's having a great time on set, and Zap2it has confirmed that he will be guest starring in the second episode of the season alongside Jeff Fahey, who starred on "Lost" as pilot Frank Lapidus.

Fahey plays Karl Sneijder, who, as the boss of a diamond company with mines in South Africa, has been investigated by the CIA in the past for alleged criminal activity. They've never been able to pin anything on him.

Hartley will star as Wesley Sneijder, Karl's handsome younger brother. A Dartmouth and Oxford-educated anthropologist, Wesley has always done his best to stay out of his brother's business, wanting nothing to do with the "world of espionage and spies."

Of course... he isn't given much choice when Karl's enemies kidnap him. Karl will be forced to seek out Carmichael Industries for help.

Don't miss the "Chuck" Season 5 premiere on Friday, Oct. 21, at 8 p.m. EST on NBC. Hartley and Fahey's episode will air the following week.