Fans of Full House mark your calendars! Famous twin Mary-Kate Olsen, who recently appeared in a few episodes of Showtime's Weeds, will guest star on ABC's hit sitcom Samantha Who?

The 22-year-old actress will appear in one episode of the good-versus-evil series starring Christina Applegate this fall. Right now, there are no plans to have the actress return for more episodes.

Slight spoilers about Mary-Kate's role on SW? coming up!

The actress, who started shooting her scenes this week, will play a self-destructive bad girl who reminds lead-character Samantha Newly of her younger self, according to a show representative who spoke with Us Magazine.

As fans of the series know, Samantha was a bad girl before she had an accident. After a few days in a coma, Sam woke up with amnesia. While she is rediscovering herself in every episode, Samantha tries to stay on the "good" path. Not surprisingly, Samantha wants to save Mary-Kate's character from her destructive life.

The episode in which Olsen will appear should air sometime in October 2008 on ABC.

[via TVTattle]