Dutch king Willem-Alexander has responded to the revelation that his grandfather, prince Bernhard was, irrefutably, a member of the German Nazi party until 1936, by saying that the past needs to be faced up to.

“I can well imagine that this news has had a big impact, and is cause for emotion, for the Jewish community in particular. But I am convinced that the past must be faced, including the less edifying parts,” the king told the press before an art award ceremony at the palace on Dam square in Amsterdam.

His decision to open up the royal archive to researchers up to September 6 1948, which covers World War II and its aftermath, is part of the reckoning with the past, he said.

“I myself could have removed things from the archive but I decided not to. I think the entire archive has to be available as transparently as possible, for the study of history.”

“The king is not shying away from the subject”, RTL Nieuws wrote, while the AD said the king had been “open” about an embarrassment for the crown that has lasted decades. Political commentator Wouter de Winther of the Telegraaf, the only Dutch paper which continued publication during the war under Nazi supervision, said the prince’s reaction had been “praiseworthy”.

Archive research by former royal archive chief Flip Maarschalkerweer uncovered the prince’s original membership card, copies of which had been found earlier in the United States.

The original document, retrieved by American officials from files in Berlin, was kept in a safe and later sent to the prince to be destroyed. For reasons unknown, he never did.

The discovery of the card, mentioned in a footnote in Maarschalkerweerd’s De Achterblijvers (Those who stayed behind) the latest publication about queen Wilhelmina’s government in exile in England, has prompted calls for an investigation into the prince’s past affiliation with the Nazi party from MPs and a number of Jewish organisations.