Fiona Shaw

True Blood has cast Fiona Shaw as a regular in the upcoming season, a show rep tells TVGuide.com.

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The Irish actress — best known in the U.S. as Aunt Petunia in the Harry Potter movies — will play Marnie, a timid storefront medium and palm reader who is taken over by a powerful witch, Deadline reports.

The 52-year-old Shaw co-starred on ABC's 2005 series Empire.

What do you think of the casting?