Below are five sneak peeks from Thursday night's all-new episode of Grey's Anatomy, "Before and After." The big Grey's Anatomy-Private Practice crossover is in full effect, with Addison & Co. at Seattle Grace with her ailing brother, Archer (Grant Show).

From the clip below, his prognosis doesn't look good ...

[video url="http://www.tvfanatic.com/videos/before-and-after-preview-3/" title="Before and After Preview #3"][/video]

Follow the jump for four more previews, in which Derek reunites with old friend Sam (Taye Diggs), Izzie gives the interns their daily assignment, Lexie pressuring Mark to go public with their relationship, and Sam and Mark poking fun at Bailey's new career path ...

[video url="http://www.tvfanatic.com/videos/before-and-after-preview-1/" title="Before and After Preview #1"][/video]

[video url="http://www.tvfanatic.com/videos/before-and-after-preview-2/" title="Before and After Preview #2"][/video]

[video url="http://www.tvfanatic.com/videos/before-and-after-preview-4/" title="Before and After Preview #4"][/video]

[video url="http://www.tvfanatic.com/videos/before-and-after-preview-5/" title="Before and After Preview #5"][/video]

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.