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.

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

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