In 1656, the court painter Diego Velázquez placed a small princess at the center of one of the most studied paintings in the world. What the painting does not show is who her parents were. They were an uncle and a niece. By the age of fifteen, she had been married to her uncle, and by the age of twenty-one, she had buried three of her children and was dead herself.

The only child she left behind would carry the highest inbreeding coefficient ever calculated for a member of the Habsburg family. Her name was Margarita Teresa, and the painting is “Las Meninas,” on display today in the Prado Museum in Madrid. Her ladies-in-waiting surround her. Velázquez painted himself on the left, brush in hand, before a huge canvas.

If you look past all of them, a small mirror hangs on the back wall. The two blurred faces in that mirror are her parents, King Philip IV of Spain and his wife, Queen Mariana of Austria. Mariana was Philip’s niece, so the king in the mirror had married his own brother’s daughter, and the little girl in the center of the room was their child. For this family, such a marriage was normal.

The Habsburgs ruled Spain and Austria and vast stretches of Europe, and they held it all together by marrying one another. Cousin to cousin, uncle to niece, generation after generation, so that the crowns would never leave the family. Every one of those marriages drew from the same small pool of blood. When geneticists later ran the calculations for the children of Philip and Mariana, they found them at a level of inbreeding comparable to the offspring of a brother and sister.

One of those children was Margarita’s younger brother, who grew up to become Charles II of Spain, the last Habsburg king of the Spanish line. Margarita was born on July 12, 1651, in the Royal Alcázar of Madrid. She escaped the severe disabilities her brother would later suffer. The accounts describe her as slender, with a weak constitution, but lively and intelligent.

Velázquez painted her again and again as she grew, eight times by one count. In 1659, one of those portraits, “The Girl with the Blue Dress,” was sent as a gift to the imperial court in Vienna. Within a year, Spain promised her in marriage to the emperor who lived there. That emperor was Leopold I.

He was her mother’s brother, which made him her uncle. His mother was her father’s sister, which also made him her first cousin. By one modern genetic estimate, he was the most inbred Holy Roman Emperor ever. The engagement was announced in 1663, when Margarita was eleven years old, and Spain made a choice here that cast a shadow over this family for decades.

Her older half-sister had to renounce her rights to the Spanish throne when she married the King of France. Margarita was allowed to keep her rights. All of Europe regarded this as a political event of enormous consequence, because it meant that a Habsburg bride in Vienna might one day pass a claim to Spain and its entire empire to her children. For the record, Spain never paid her dowry.

On April 25, 1666, at the age of fourteen, she married by proxy in the Alcázar, with someone standing in for the groom. Then came the long journey to Austria. In late November, she met Leopold for the first time at Schottwien, on the road south of Vienna. In December of that year, now fifteen years old, she married him in person.

Vienna celebrated her with festivities that lasted nearly two years. In January 1667, Leopold took part in a massive equestrian ballet in the courtyard of the Hofburg Palace, a spectacle designed around her name, since Margarita is the Latin word for pearl. On her seventeenth birthday, the court presented an opera called “Il pomo d’oro” — The Golden Apple — one of the most lavish productions of the age. By most accounts, the marriage was happy.

The two shared a love of music, and she was said to call her husband “Uncle. ” She remained Spanish to the bone, surrounded by Spanish servants, and barely learned German. Then the pregnancies began, and they almost never stopped. Her first son, Ferdinand Wenzel, was born in September 1667.

He died the following January, not yet four months old. In January 1669, she gave birth to a daughter named Maria Antonia. Remember that name well, because she is the person this entire story moves toward. A year later, in February 1670, Margarita went into early labor, and the boy she bore, Johann Leopold, died the day he was born.

During that birth, she made a vow. If she survived, she would work to expel the Jews from Vienna. She did survive. That same year, the Jewish community of Vienna was expelled.

Their synagogue was demolished, and the district where they had lived was renamed Leopoldstadt, after her husband. It still carries that name to this day. It is a grim detail, and it shows how much weight a single royal birth carried inside that palace, and who ended up paying for it. In February 1672, she gave birth to another daughter.

The child lived only two weeks. Count the result. Five years of marriage, four children born, three buried, and by some accounts two more pregnancies lost before they came to term. In early 1673, she was pregnant again.

She had suffered from a swelling in her throat since childhood, and that winter she caught a chest infection on top of it. The standard German biography concludes that she died of suffocation. She died in Vienna on March 12, 1673, at the age of twenty-one. Other accounts attribute her death to sheer exhaustion after nearly six years of almost continuous pregnancy, and the exact cause remains debated.

Then comes the cruelest line in her entire story. Esaias Pufendorf, the Swedish envoy at the imperial court, wrote in his dispatches that the people of Vienna regarded her passing in her twenty-first year as a stroke of luck for the Austrian line. A young empress dies while pregnant, and the talk in the palace corridors is that the dynasty had been fortunate. Leopold wept for her as the only “Margarita” of his life, and within months he was arranging his next marriage.

Her only surviving child was a four-year-old girl living in the Hofburg Palace. That girl inherited everything her mother owned, including the claim to the Spanish throne. Her family tree was even more tangled than her mother’s. Her father was her mother’s uncle.

Her mother was herself the daughter of an uncle and niece. If you trace the branches upward, the same people appear in different positions. On her father’s side, her grandparents were Emperor Ferdinand III and Maria Anna of Spain. On her mother’s side, the same couple served as her great-grandparents.

A normal family tree has eight great-grandparents. Hers had only six. By the time she was seven years old, the family had already chosen a husband for her. In 1676, a marriage contract was signed promising her to her mother’s brother, Charles, the King of Spain.

It would have been the third uncle-niece marriage in three generations. It never took place. But for about twenty years, because Charles had no children, the Spanish court treated this girl in Vienna as the heir to the entire Spanish Empire. The people who met her described nothing monstrous.

The surviving accounts say she was quiet and reserved, shy and delicate. She was not a great beauty, but striking in her own way. There is no reliable record of the famous Habsburg jaw, or any of the deformities one might expect from a family tree like hers. In 1685, at the age of sixteen, she married Maximilian Emanuel, the Elector of Bavaria, in Vienna.

As part of the agreement, she renounced her claim to the Spanish throne, keeping only the Spanish Netherlands, which were promised to her new husband. The marriage soured. The standard biography says Maximilian Emanuel treated her unbearably, and she could not keep his mistresses away from him. Then her body began to repeat her mother’s story.

She gave birth to three sons, and the first two did not survive infancy. In 1692, she was pregnant again when her husband left for Brussels. She refused to go with him. Instead, she returned to her father in Vienna, and on October 28, 1692, in the Hofburg Palace, she gave birth to a boy named Joseph Ferdinand.

This time the child lived. But she never regained her strength. The weeks passed. She sank into a deep depression.

On Christmas Eve, 1692, she died at the age of twenty-three. The exact cause was never recorded clearly enough to be determined. The theories you will find online, from childbed fever to depression, are only guesses. Before her death, she made sure of one thing.

In her will, she renounced the Spanish crown once again. She excluded her husband entirely. She left everything she had to her infant son, offering only a few keepsakes to the Bavarians. She asked to be buried beside her mother in the Imperial Crypt in Vienna.

So just how inbred was she really? In 2013, two geneticists, Francisco Ceballos and Gonzalo Álvarez, reconstructed the Habsburg family tree across more than twenty generations and over four thousand people. They calculated the inbreeding coefficient for each individual. This number is the probability that the two copies of a gene you inherit are identical because they come from the same ancestor.

For the child of unrelated parents, the number is close to zero. For the child of first cousins, it is about 0. 06. For an uncle and niece, 0.

125. For a full brother and sister, 0. 25. Maria Antonia’s result came out at 0.

3053. That is the highest figure they found anywhere in the Habsburg line. Higher than her uncle Charles, who scored 0. 254.

Higher than what you would expect for the child of a brother and sister. The reason is that these ratios accumulate. Her parents were uncle and niece and first cousins at the same time, and every marriage in the generations before them drew from the same narrow circle of people. So each marriage pushed the number a little higher.

Now the truth must be stated, because it matters. This number does not come from her DNA. Nobody has examined her remains. It is calculated from family trees, and part of the database behind it was built from genealogy websites, including Wikipedia.

So 0. 3053 is only an estimate on paper. But it is a peer-reviewed estimate, and nobody else in that family scored higher. What the research points to is a damage you cannot see in a painting.

Between 1527 and 1661, nearly three out of ten children born into the Spanish royal family died before their first birthday, at a time when ordinary Spanish villagers lost one in five, and half of those royal children never reached the age of ten. In a study published in 2024, the same research team looked at 124 Habsburg marriages and asked what inbreeding did to the mothers. The more inbred the mother, the younger she tended to die, and the higher her risk of dying in the four weeks after giving birth. That study cannot tell you what killed either of these two women.

It describes a pattern across the whole family. But put these two women beside that pattern. A mother who died at twenty-one while pregnant again, and a daughter who died at twenty-three two months after childbirth, having already lost two sons before that. Her son’s story was short too.

In 1698, her uncle Charles, who had no children, signed a will naming the boy his heir. On February 6, 1699, the boy died at the age of six. Most sources point to smallpox, and the poisoning rumors were never proven. His death brought the diplomats back to the negotiating table.

When Charles died in 1700, Europe fought the War of the Spanish Succession over his throne for thirteen years. In the Imperial Crypt, the coffin of Margarita’s daughter carries a Latin inscription that mentions four things: her birth, her marriage, her childbearing, and her death. That was the entire life the family had planned for her. And it was the same life they had planned for the little girl in “Las Meninas.

” The most inbred Habsburg ever measured was not the “Bewitched King” everyone remembers. It was his niece, the quiet girl from Vienna. We have now seen what two successive uncle-niece marriages did to a mother and her daughter.

But they were just two stories in a dynasty that kept intermarrying for generations, and the damage did not look the same on everyone.