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Royal Coster
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MM / INCH (Circumference)
48 / 1.89 48 4½ 8
49 / 1.93 49 9
50 / 1.97 50 K 10
51 / 2.01 51 L 11
52 / 2.05 52 6 12
53 / 2.09 53 13
54 / 2.13 54 14
55 / 2.17 55 O 15
56 / 2.20 56 P 16
57 / 2.24 57 8 17
58 / 2.28 58 18
59 / 2.31 59 R 19
60 / 2.36 60 9 S 20

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The Story of King Willem III - Royal Coster Diamonds

The Story of King Willem III

Willem Alexander Paul Frederik Lodewijk, also known as King Willem III of the Netherlands was our king from 1849 until his passing in 1890. In 1862, he visited our diamond polishing factory. However, King Willem the third was not ‘just another royalty’ visiting Coster. In fact, he and the original owner of Royal Coster Diamonds, Martin Coster, were actually quite close. Dare we say: even friends?

About King Willem III

Born in 1817, King Willem III was the son of King Willem II and Anna Paulowna. Willem didn’t want to become king in the first place. But this changed when his father died in 1849. Willem III decided to take his responsibility and accepted anyway, knowing it was his father’s wish. In 1839, he married his cousin Sophie van Wurtemberg. Unfortunately, it was not a happy marriage. Perhaps due to his young age (22) or the fact that he quite suddenly became king. But Willem still had some wild oats to sow. He expressed this in extra-marital affairs and often-erratic behavior. Eventually, Sophie left him in 1855. This was very remarkable at that time. The king and queen had three sons together. Yet none of them would ever reign. They all died before their father.

portrait from King Willem III with Queen SophieSketch from King Willem III and his Queen Sophie van Wurtemberg (1839)

King Gorilla

In earlier years, King Willem III did not show his best sides to the Dutch people. All the (extra-marital) scandals and his bad temper did not make him popular. The people even had a nickname for him: “King Gorilla”. However, between 1855 and 1861 he made it up to his country. When the dikes broke, many people lost their loved ones and their homes. The king rushed to the disaster area and spoke to the victims. He stayed with them for days and spent a lot of personal attention to them. He arranged clothing, food, coffee, and tents and donated money to help the survivors get back on their feet. This created a lot of goodwill. After ’61, King Willem III was often in Paris.

02. Aanblik op het bezoek van Koning Wilem III aan de dijkdoorbraak te Brakel, Watersnood 1855. Kleurenlitho, Tresling & Co., 1888 - prentVisit from King Willem III at the dyke breach and flood in 1855. Color lithograph by Tresling & Co. made in 1888.

Parisian diamonds

In 1851, Martin Coster, owner of Coster Diamonds, moves to Paris. Here, he sets up a cutting factory as well. A sir called “Joseph Halphen” was the most prominent and possibly the only diamond provider in Paris. He outsourced the entire processes of diamond sorting and cutting to Martin Coster. Perfect timing, because Coster just set up a branch in Paris. This gave Coster a monopoly position for all the diamonds in Paris. Back then, Coster Diamonds had the exclusive right to provide all diamonds for the large jewelers in Paris; like Tiffany & Co. and Boucheron.
Administration papers of diamond trading and polishing in France (1843) Administration papers of diamond trading and polishing in France (1843)

In 1862, King Willem III visits the Coster diamond polishing factory in Amsterdam. This is the first documented connection between Coster and King Willem III.

The King and Coster in Paris

Martin Coster was a member of the Dutch organizing committee for the 1867 World Exhibition in Paris. But he also participated. His participation was a replica of his polishing factory in Amsterdam. At that moment, the factory was the largest in the world. It earned him a gold and silver medal at the “Champs de Mars”. The factory was one of the highlights of the exhibition and attracted
worldwide media attention.
1867 Tallerie de diamants (From the Archives Nationales, Paris)Tallerie de diamants, Coster’s polishing factory, from the Archives Nationales, Paris (1867) - Source:

replica of diamond polishing factory royal costerMartin Coster’s participation for the “Exposition Universelle de 1867” in Paris. He built an exact replica of his diamond factory in Amsterdam. For this factory, Martin also received a Knighthood in the Legion d’Honneur by Napoleon III, who was a personal friend of King Willem III. - Source:

Coster’s honorary titles

In 1868, Coster was appointed by King Willem III as Consul General of the Netherlands in Paris. Willem III also made him a knight in the order of the Netherlands Lion. In 1872, the King made Martin Coster Commander in the Order of the Oak Crown. There are two reasons plausible for why the king granted Coster this title. Possibly because of his role during the revolution
of the French commune in 1871. Instead of fleeing the city, Coster remained in Paris and played his diplomatic role. President Thiers had plans to tax rough diamonds. Those plans would hit the Amsterdam diamond industry hard. But they were prevented because of Coster’s intervention.

A personal connection

Another viable option is that King Willem III used the Oak Crown as his personal order. He could bestow without permission of the government. The king spent a lot of time in Paris. So it is thinkable that Martin Coster as Consul General was involved in many aspects of the King’s private life, for which the king was grateful. One thing is sure: the connection between the king and Martin Coster was more than strictly professional.

A new queen for his majesty

In 1877, King Willem’s ex-wife Sophie passed away. This meant the king could (morally) find someone else. King Willem III was a lover of arts and started an affair with the Parisian opera singer Emilie Ambre. He wanted to marry her. Even if it meant abdicating his throne and moving to Paris for good. This would cause serious problems. There were only a few male members of the House of Orange left. And none of them were suitable kings. They were either unwilling to succeed the throne, unlikely to ever marry, or too old to provide another heir to continue the Dutch monarchy. This meant the King had to remarry, and fast! But this was easier said than done. The king's reputation in Europe was dismal. But he knew what he had to do. So in 1878, he set upon a European tour to find himself a new Queen.

The next World Exhibition

While the King was searching for his future bride, the Paris Universal Exhibition of 1878 happened. Martin Coster, as Delegated Commissioner, was the lead in the Dutch participation. The King’s brother, Prince Henry, was honorary chairman of the Dutch organizing committee. Coster added to the international prestige of Holland by organizing Dutch horse races in the Bois de Boulogne. The 2-day event was a huge spectacle. Even general Mac-Mahon and many other dignitaries were present. Martin Coster invested large amounts of his own money in the Dutch pavilion.

Another connection between Coster and the king

One of the exhibits in the Dutch pavilion was the silver-gilt cup in a gothic style which King Willem had given to Martin Coster. Free champagne and cigars were provided for everyone, including, according to one news report, the King’s son the Prince of Orange. Shortly after the races, a French newspaper reported that the King had bestowed upon Martin Coster the title of Count, although no record of this ennoblement is available and Coster never used this title.

Sketch from orse races in the Boise de BoulogneMartin Coster organized Dutch horse races in the Bois de Boulogne, during the 1878 World Exhibition. - Source:

Another medal for Coster

Coster won a silver medal for his participation in the 1878 exhibition. Although he did under a different name: Alexander Daniels. Daniels was the Director of Coster Diamonds at that time. De factory was owned by Martin Coster, but operated under Daniels’ name. One of the marvels of Daniels’ exhibit was the large faint yellow diamond with King Willem III’s portrait engraved in it. The seemingly impossible engraving was done by the Amsterdam engraver and medallist M.C. de Vries. It took him 5 years to finish the job. After the World Exhibition, Martin Coster gave the medallion with King Willem’s portrait to the King himself as a gift.

medallion King Willem III with portraitThe diamond medal made by one of Coster’s diamond polishers and given to His Majesty King Willem III by Martin Coster around 1879. - Source:

A new queen

During the exposition in Paris, the King found his bride in the minor German Principality of Waldeck and Pyrmont. Here, he spent much time in the fall of 1878. Princess Emma was one of three sisters available. She was the only one willing to marry the King to prevent the House of Orange from going extinct. Initially, Willem wanted to marry the oldest daughter, Pauline. But then he really hit it off with her younger sister Emma. Besides a bow brooch and pendant the King gave Emma as engagement presents, he gave her a medallion. It was the engraved diamond portrait he received from Martin as an engagement present.

King Willem III and his young bride EmmaPortrait of Princes Emma and King Willem III (1879)

Symbolization of the medallion

Coster’s gift to King Willem III is even more thoughtful than you might initially think. The medallion is completely set with rose diamonds, a cut that was best known as ‘Dutch Rose Cut’. The magnificent gift confirms the close relationship between the King and his Consul General in Paris. It raised the profile of the Netherlands on the international stage. Consequentially, this was also the meaning of the gift of this medallion by the King to Queen Emma. Romance was not part of this alliance.

The king becomes a family man

After his marriage to Emma, the king lost his focus in Paris and instead enjoyed his family life. In August, his daughter Wilhelmina was born: the last hope for continuing the dynasty.

King Willem III with his (new) familyPainting of King Willem III, his wife Emma and their daughter Wilhelmina

On February 1st, Martin Coster died in Paris. He was buried in the Jewish section of Montmartre in Paris. The country was in mourning and newspapers wrote: “Holland lost its most popular Consul (…) it was generally known how Mr. Coster was a Consul who could be desired, always ready to defend with his person and his great wealth, the interest of his country and countrymen, and raise the honor of the fatherland.

Grave Martin Coster from Royal Coster Diamonds in ParisMartin Coster’s grave in the Montmartre cemetery (pictures were taken in 2017)

The end of an era and a new beginning

The Dutch government decided not to find a new Consul General. It is the last confirmation that Coster and the King had a special relationship. Ten years after Martin’s passing, King Willem III also passes away. His young daughter Wilhelmina, age 10 at the time, became queen. She saved the family name and her father’s kingdom. Wilhelmina was the great-grandmother of our current king, Willem-Alexander.

Emma van Waldeck-Pyrmont met haar dochter Wilhelmina in rouw (1890)Emma van Waldeck-Pyrmont with daughter Wilhelmina in mourning (1890)

Original research: Pauline Willemse
Source: Erik Schoonhoven

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