King Willem-Alexander of the Netherlands is set to make a formal apology for slavery after it was revealed the Dutch monarchy earned £850million from its colonial military conquest.

King Willem-Alexander will make the formal apology on July 1, when the country will mark the 160th anniversary of the end of slavery on what is known as Keti Koti, or Emancipation Day, according to Mail Online.

The Princes of Orange, including William III, who became the King of England, helped to establish a policy of exploitation, slavery, and forced labour in Asia and the Caribbean, according to a study commissioned by the Dutch government. 

The new study, titled 'State and Slavery', was presented to MPs last week. It found that the House of Orange earned the equivalent of €1billion (£853million) in today's money during the Dutch slave trade and the era of colonialism. 

It comes after King Charles backed a landmark UK study into the monarchy's involvement in the slave trade.

The research is expected to analyse previous rulers' involvement with slave-trading entities, including the Royal African Company and its deputy governor, Edward Colston, whose statue was thrown into Bristol Harbour by anti-racism protesters in 2020. 

Hanke Bruins Slot, the Dutch home affairs minister, said the findings of the new study presented a 'confrontational and very painful picture' of the early Dutch state's involvement in an 'unprecedented scale of slave trade and slavery', according to The Times.

She added that the 'story' should have been told 'earlier.'   

The Netherlands did not abolish colonial slavery until 1863, making it one of the last countries to do so. 

Raymond Schutz, a historian who worked on the new report, estimated that William III and his successors earned '3.04million guilders in colonial profits'.

Speaking to Dutch newspaper Algemeen Dagblad, Mr Schutz said that amounted to €545 million (more than £464million) in today's money.