The Dutch Royal household has confirmed that Prince Bernhard - prince consort for decades after World War II and husband of former Queen Juliana - was a member of the Nazi party.
The membership card for the NSDAP, the German National Socialist Party attributed to Prince Bernhard, dates back to 1933.
Historian Flip Maarschalkerweert, former director of the Royal Household Archives, discovered the map while making an inventory of Prince Bernhard's private archives at the royal Soestdijk Palace, located in Utrecht.
Prince Bernhard - who died in 2004 aged 93 years old - had repeatedly denied having been a member of the Nazi party, after revelations first emerged in the media in 1996.
"I can declare it with my hand on the Bible: I was never a Nazi", he said in an interview published a few days after his death in the national newspaper De Volkskrant.
Adding that he had "never paid a membership fee to the party and never had a membership card".
Prince Bernhard was living in Berlin when he joined the party. He became prince consort to Queen Juliana in 1948 and was the father of Queen Beatrix, and grandfather of the current Dutch King Willem-Alexander.
"I can imagine that the news has had a major impact and that it has aroused many emotions, particularly within the Jewish community", King Willem-Alexander told television cameras on Thursday as he arrived at the Dam Palace in Amsterdam.
Part of the lower house of the Dutch parliament is demanding that the government launch an enquiry into Prince Bernhard's Nazi past, a demand so far rejected by the outgoing Dutch Prime Minister Mark Rutte.
The CIDI, a Dutch Jewish organisation, is also calling for an enquiry, citing "a new revelation that adds another black page to a painful part of recent Dutch history".
Declining royal popularity
The revelations surrounding Prince Bernhard come as the royal family's popularity has been falling for several years.
According to an Ipsos poll published in September, only 38% of Dutch people still "really trust" the King, compared with almost 80% in 2020.
Some 26% of those questioned stated they want the Netherlands to become a republic.
In autumn 2020, while the government was asking the Dutch to avoid travelling because of the Covid-19 health crisis, the royal family tried to sneak off on holiday to Greece. This sparked a wave of indignation across the country.