The rolling green lawns of a 12th-century castle perched on a windy stretch of south Wales coastline usually dotted with sheep hosted not one but two kings of Europe last weekend.

The purpose of the visit to St. Donat’s by the royal families of Spain and the Netherlands was the graduation of their daughters from UWC Atlantic College, a high school housed in a remote castle once owned by the newspaper tycoon William Randolph Hearst.

Under unusually bright blue skies on Saturday, Princess Alexia of the Netherlands, 17, smiled in a white linen trouser suit flanked by her parents, Queen Maxima and King Willem-Alexander (a former Atlantic College student himself) in a photograph posted on Instagram.

Princess Leonor of Asturias, who is also 17 and the heir to the Spanish throne, wore a scarlet red button down blazer dress with split sleeves as she posed for selfies with her parents and younger sister Princess Sofia, who is set to start there in September.

The scene was a reflection of how Atlantic College, which is part of the United World Colleges group, has become the school of choice for many young royals. It increasingly draws students who may have once gone to better-known places like Eton College in the shadow of Windsor Castle or Institut Le Rosey on the edge of Lake Geneva in Switzerland, considered the most expensive boarding school in the world.

Other recent alumni of the school, which educates students for their final two years of high school, include Princess Elisabeth, Duchess of Brabant, who is Belgium’s future queen. She graduated in 2021 and went on to study at Oxford.

The British press has pondered whether the British royal family may break with tradition and send its own young heirs to a school that has recently educated several future queens of Europe.

One Enduring Tradition: Discretion

Although UWC may have more of an updated atmosphere and curriculum than its more traditional counterparts, it does appear to subscribe to at least one very old — and very royal — convention: the art of being tight-lipped. The school did not respond to numerous requests for comment for this article, and seems to mostly avoid speaking to reporters.

Tori Cadogan, the education editor of the British society magazine Tatler, said that the appeal of Atlantic College has largely to do with an optimistic ideology rooted in “deliberate diversity” and world peace. The school enrolls plenty of children of royalty and other wealthy families, but there are also a significant number of less privileged students.

Tuition is expensive: about $82,000 for the two-year international baccalaureate program.

Many students receive financial aid, however, including a significant cohort who are victims of war or refugees on full scholarships. Their applications go to the U.W.C. national committee, which then assigns the students to Atlantic College campuses around the world, perhaps in Thailand, Costa Rica, Norway or the United States.

Last week, the Dutch royal family announced that Princess Ariane of the Netherlands, the third and youngest daughter of King Willem-Alexander and Queen Máxima, would attend the United World College Adriatic near Trieste, Italy.

Atlantic College opened in 1962 — the height of the Cold War — and the idea to make a diverse student body a priority came from Kurt Hahn (who founded Gordonstoun, King Charles’s alma mater). He decided a new form of teaching, which emphasizes responsibility, internationalism and democracy, was needed to avoid another world war.

A statement on the school’s website says the mission of the school is “to bring together young people from around the world to help create an atmosphere for peaceful coexistence between cultures and nations.”

Leave the Rolex at Home

What, then, does a teenage princess do with her days at Atlantic? According to the “A Day in the Life” section of the school website, classes run from 8 a.m. to just after 1 p.m., with afternoons left open for community service at local hospitals and schools, as well as activities like kayaking, archery, planting in the greenhouse or working on the school farm, or even serving on the school’s own lifeboat service. (According to the BBC, the widely used Rigid Inflatable Lifeboat was invented by students at the school in the early 1960s.)

Cellphone reception is said to be ghastly (likely to the delight of teachers and parents). “E.D.W.s” (excessive displays of wealth) are banned, which means no expensive watches or designer gear.

Louise Callaghan, a former student who is the Middle East correspondent for the Sunday Times, wrote a column in 2018 about her time at the school. She said it forced many students to “get very used to being around, and getting along with, people who are nothing like you.”

These included, she wrote, “refugees from West Africa, Brits from across the social spectrum, California hippies, religious Malaysians.” Learning how to interact with such a diverse group, she said, “is a useful life skill — one, I imagine, you do not gain at a normal private school.”

She also had a more lighthearted take on her time there. Atlantic College, she wrote, was a little like “a hippie Hogwarts.”