6/8. Warhol: Denied. The joy of some collectors at owning what they believed to be genuine Andy Warhol works has been ruined by the artist's authentication board's declaring them fake. They speak of their disillusionment here as Alan Yentob visits New York to investigate acquiring art by the "Pope of Pop", while Warhol collaborators reveal his unusual working methods. Producer Chris Rodley ; Series producer Janet Lee