The royal household of the Netherlands has confirmed the authenticity of a Nazi membership card belonging to the Dutch king’s grandfather, bringing an end to the decades-long suspicions that had swirled around Prince Bernhard. Claims of ties between Bernhard, a German aristocrat who married into the Dutch royal family in the 1930s, and the Nazi party surfaced in the late 1990s after a Dutch historian said he had found a copy of the card in a US archive. Bernhard, who was prince consort until 1980, adamantly denied being a Nazi. “I can swear with my hand on the Bible: I...