Queen’s Day is a national holiday in the Netherlands, the Netherlands Antilles, and Aruba on 30 April or on 29 April if the 30th is a Sunday. Queen’s Day celebrates the birthday of the Queen of the Netherlands and is supposed to be a day of national unity and “togetherness”. The tradition started on 31 August 1885, on the birthday of Princess Wilhelmina, later Queen Wilhelmina. Since 1949, after the accession of Queen Juliana, Queen’s Day is Queen Juliana’s birthday on 30 April. Although Queen Beatrix’s birthday is on 31 January, she officially celebrates her birthday on 30 April.(via)