1 The new king sewed his own wetsuit

Willem-Alexander spent two years living in rainy Wales in the mid-1980s when he was a student at an international sixth-form college. His mum, Queen Beatrix, came to Atlantic College near Bridgend to drop her son off. Dutch TV crews were invited along to record the moment and were occasionally spotted afterwards lurking in bushes. The college, known as AC, is home to students from more than 90 countries. (There was a relatively big Dutch contingent; its slogan went: “If you’re not Dutch, you’re not much.”) AC has a strong idealistic ethos, with an emphasis on international understanding; most students are on scholarships. The campus boasts a Harry Potter-style medieval castle, a jousting field, and sweeping views of the Bristol Channel. Students study the International Baccalaureate. The teenage prince joined AC’s student-crewed RNLI lifeboat service, which was sometimes called out for rescues; you had to sew your own wetsuit. He was also a pretty decent squash player. A laidback figure, Willem had a reputation as a party-lover and a bit of a Romeo. He dated several female students from Latin America and nobody was very surprised when he later married an Argentinian woman. LH

2 The Dutch royal family costs more than the British one

For a supposedly low-key, Scandinavian-style bicycling monarchy, the Dutch royal family come pretty expensive. According to last year’s annual study by Herman Matthijs, professor of administrative science and public finances at Ghent University, the House of Oranje-Nassau costs the country’s taxpayers £31m a year. That’s more than any other royal family in western Europe – including, for the first time, the House of Windsor, whose direct costs were reduced by 16% last year to around £29.7m.

The overall bill for the Dutch monarchy is four times the cost of the Spanish royal family – and proportionately even dearer, because the Netherlands’ population of 16.7 million is only a third the size of Spain’s and a quarter the size of Britain’s. The expenditure is divided between allowances paid to the monarch and the heir apparent (in 2010, Queen Beatrix, Prince Willem-Alexander and Princess Máxima received €7.1m), expenses incurred in the performance of official duties (€27m), and other expenses related to the management of the royal house (€5.7m). The Dutch royal family is also very rich. In 2009, Forbes magazine estimated Queen Beatrix’s wealth at $200m, noting reports that the Queen and her family had been hit by declines in real estate and equity investments but may also have lost up to $100m in Bernie Madoff’s Ponzi scheme – although the royal house has consistently denied that allegation. JH

Queen Beatrix (centre), with her husband Prince Claus and her sons the now King Willem-Alexander (right), Prince Constantijn (second right) and Prince Johan Friso (currently in a coma following a skiing accident). Photograph: Reginald Davis/Rex Features

3 Willem has a reputation

King Willem-Alexander was a bit of a lad, earning himself the nickname Prins Pils (Lager Prince) for his student beer-drinking, and once drove his car into a ditch. JH

4 The monarch’s birthday is celebrated with a car boot sale

From next year, Koninginnedag, or Queen’s Day, will become Koningsdag, or King’s Day. It’s an endearing if slightly crazed Dutch national holiday celebrated every year since 1948 on 30 April (or thereabouts). It marks the birthday of Beatrix’s mother, Juliana, and Beatrix chose to celebrate her birthday on the same date. Koninginnedag is, strikingly, the only day in the year when the Dutch are allowed to sell whatever they like, wherever they like, which essentially means the country becomes a giant fleamarket. That one of world history’s greatest mercantile nations should choose to celebrate its monarch’s birthday by staging a kind of national car boot sale is, somehow, pleasing. JH

5 They don’t wear crowns

In fact they don’t even have a coronation. Willem-Alexander became king the moment his mother signed her abdication papers, and even at the formal inauguration ceremony, the crown, orb and sceptre were only displayed on a table. The crown itself, by the way, was made out of gold-plated silver in 1840, and uses fake pearls and jewels made from fish scales, glass and coloured foil. LB

Koninginnedag was bigger than usual this year. Photograph: Demotix/Corbis

6 Part of their kingdom is in the Caribbean

Holland is only a part of the Netherlands, of course – and not even the majority of it. (Calling the country “Holland” is like saying “England” instead of “Britain”.) But the Netherlands itself is only a part of the Kingdom of the Netherlands, which also includes the two and half Caribbean islands of Aruba, Curaçao and Sint Maarten. The 280,000 or so people who live on them now have a new king too. LB

7 They have a habit of marrying undesirables

The former Queen Beatrix caused outrage in 1966 when she chose as her husband Klaus-Georg von Amsberg, a member of the German nobility and former conscript of the Hitler Youth and the Wehrmacht. The ceremony itself saw angry chanting and smoke bombs being thrown, in protest at one of the country’s former occupiers joining its establishment. Then in 2002 Willem-Alexander married Maxima Zorreguieta Cerruti, the Argentinian daughter of a man who had been one of dictator Videla’s ministers during the dark years of the military junta. Sensibly, he didn’t attend the wedding. Both partners subsequently proved to be good choices, however, and grew to be adored by the Dutch public. LB

8 The new king is 889th in line to the British throne

Give or take. These things are difficult to count with certainty. But then the royal family in the Netherlands are related to just about every other monarch in Europe. Through his great-great-great-great-great-great-great-grandfather Jan Willem Friso, Prince of Orange, King Willem-Alexander is a cousin of Margrethe II of Denmark, Albert II of the Belgians, the Grand-Duke of Luxembourg, Harald V of Norway, Juan-Carlos of Spain, Albert II of Monaco, and our own Queen Elizabeth II. LB

9 Their children go to state schools

When they speak, they do sound identifiably posh to other Dutch speakers, but in their choices the country’s royals have been firm egalitarians. King Willem-Alexander attended state schools, and so do his daughters Catharina-Amalia, Alexia and Ariane. His wife Queen Maxima is even registered there as a “lice mother”, with responsibility for inspecting children’s hair. LB

The Dutch crown is made of gold-plated silver, with ‘gems’ made of glass and fish scales. Photograph: Lex Van Lieshout/Pool/EPA

10 They have normal jobs

Before the skiing accident that has left him in a coma, Willem-Alexander’s younger brother Friso (who renounced his royal title in order to marry his wife Mabel, whom parliament might not have approved) was a banker and then the chief financial officer of Urenco, a nuclear fuel company. The youngest brother Constantijn works for the Rand Corporation, a policy think tank. LB

11 They are a bit political

As in Britain, the Dutch royals are expected to express no political opinions and to sign whatever parliament puts in front of them, and generally they do. When Queen Beatrix visited mosques in Oman and Abu Dhabi last year, however, she was criticised for wearing a headscarf by Geert Wilders, the leader of a popular anti-Islamic party. In response, she told reporters that the row was “nonsense”, giving a fairly good indication of where her sympathies lie. LB

12 They are determined to be groovy

King Willem-Alexander does not wish to be called Willem IV, he says, because he doesn’t want to be labelled with a number. It has been suggested that his real motive is to avoid being called “vier” (four) because it rhymes with “bier” (beer), which would make the temptation to call him “Willem Bier”, following his previous nickname “Prince Pils”, almost irrestible. His father, Prince Claus, was so committed to informality that he became famous for his condemnation of tie-wearing. He first made his feelings known at an awards ceremony for African fashion designers, when he announced his contempt for this “snake around my neck” – a statement that has since become known as “The Declaration of the Tie”. LB

• This article was amended on 2 May 2013 to clarify that the Dutch Sint Maarten is only half of an island. The other half is the French overseas collectivity of Saint Martin.