Deadline reports that actress Fiona Shaw has been added to the cast of HBO's True Blood as a series regular for Season 5.

Shaw, who is best known for playing Aunt Petunia in all of the Harry Potter movies, will portray Marnie on the popular vampire series, a timid medium who is taken over by the spirit of a powerful witch.

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The character had originally been geared towards a younger actress, but is now being retooled to fit Fiona Shaw.

It wasn't clear when production would start on True Blood's fifth season, or when the season would premiere on HBO.