Prinsjesdag (Prince’s Day) originally marked the birthday of Stadholder Prince William V (1748-1806) on 8 March.
In the Patriot Era, it was a popular holiday, providing an opportunity for demonstrations of loyalty to the House of Orange. This is probably why the name was chosen in the 19th century for the ceremonial opening of Parliament.
The Constitution stipulates the day on which Prinsjesdag is to be held. But it has not always been held on the third Tuesday in September.
In the 19th century, it was held on the first Monday in November and later on the third Monday in October. When annual budgets were introduced in 1848, more time was needed to debate them. So the opening of Parliament was brought forward to the third Monday in September. An amendment to the Constitution in 1887 moved the day from Monday to Tuesday so that members of Parliament from distant parts of the country did not have to leave home on a Sunday.
In 1983, the duration of a parliamentary session was changed from one year to four years. So since then, Prinsjesdag has no longer marked the official opening of the parliamentary year. Nevertheless, the third Tuesday in September remained the day the Constitution stipulates for the delivery of the Speech from the Throne.