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Mary-Kate Olsen is getting back to her roots. 

No, not her blondish locks.

M-K will be guest starring on ABC’s show Samantha Who? in the fall – tentatively skedded to appear in one ep.

Star Christina Applegate who plays titular Samantha will try and save a confused Olsen, a self-destructive bad girl. 

The series premise is Applegate’s character is an amnesiac trying to discover the mysteries of her life — kind of like a chick-lit version of Memento but without the mayhem and just the comedic aspects of good-versus-evil.

M-K was last on Showtime’s  Weeds  tormenting Silas.