“True Blood” star Alexander Skarsgard is set to topline Warner Bros.’ “Hidden,” which twin brothers Matt and Ross Duffer will direct from their own spec script.Project is an elevated horror-thriller about a family hiding in a bomb shelter after escaping a mysterious outbreak. Roy Lee, Mason Novick, Lawrence Grey and Richard Zanuck will produce, while John Middleton and Sebastian Aloi will exec produce. Jon Berg will oversee the project for Warners. WB acquired the Duffers’ spec late last year in a competitive situation. Deal contained progress-to-production language, indicating that studio was anxious to start filming, rather than allow the project to languish in development. Skarsgard, who recently appeared in Lars von Trier’s “Melancholia” and Rod Lurie’s remake of “Straw Dogs,” next stars in Peter Berg’s Universal tentpole “Battleship.” Thesp recently wrapped a pair of indies — Zal Batmanglij’s thriller “The East” and Henry-Alex Rubin’s “Disconnect.” Skarsgard is repped by CAA, Principal Entertainment and attorney Gretchen Rush.