'Grey's Anatomy' casts Neve Campbell as Derek's sister

neve-campbell-scream-4-premiere-getty.jpg "Grey's Anatomy" leading man Derek Shepherd ( Patrick Dempsey) has quite a family. Between his father's murder, his complicated relationship with his mother, and his four sisters, there are lots of stories to tell. We've already met his sister Nancy ( Embeth Davitz), and of course Amelia ( Caterina Scorsone) is a regular on the spin-off "Private Practice."

Now, we're about to meet a third sister. Neve Campbell has been tapped to play one of Derek's two remaining siblings -- we're just not sure which one! We've heard of Kathleen, who is a psychiatrist, so it could be her, or Campbell could play the fourth sister, whose story remains a mystery to viewers.

Of course, she and Dempsey have worked together before -- he played her boyfriend, Detective Mark Kincaid, in "Scream 3." (Don't feel bad if you didn't remember that. We're still trying our best to forget "Scream 3" ever happened.)

TVLine reports that the actress has signed on for at least a two-episode arc. She'll be arriving just as Derek is struggling to come to terms with the idea that he may never operate again. In upcoming episodes, the brilliant neurosurgeon will get a bit of a demotion as he takes on a teaching role at the hospital, still unable to use his injured hand in the operating room.

Campbell, who welcomed her first child this summer with boyfriend JJ Field, is currently starring in Encore's miniseries, "Titanic: Blood and Steel."
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