It’s All in the Family: 20 Members of Royal Families Who Married Relatives

Cleopatra VII became co-regent alongside her younger brother Ptolemy XIII after their father’s death, and according to Ptolemaic custom, this arrangement entailed not only the sharing of power but also marriage. It seems as though this was a dynasty that had ceased to distinguish between family management and governance—which, to be honest, was somewhat of a hallmark of the Ptolemies. 

After the death of Ptolemy XIII, Cleopatra resumed this pattern and reigned alongside another of her younger brothers, Ptolemy XIV, who also became her husband. At this point, this system no longer seemed so much an exception as a genuine court policy: keeping the throne within the family, however bewildering the management of family affairs might become. 

Tutankhamun married Ankhesenamun, a close relative of the royal family generally described as his half-sister, at a time when the Egyptian monarchy considered lineage and divinity to be closely linked. The result was one of those marriages that make the ancient monarchy seem very distant—until one recalls the number of subsequent dynasties that continued to follow this same fundamental logic. 

Philip II’s fourth wife, Anne of Austria, was not simply another marriage within the Habsburg dynasty, but his own niece—the kind of dynastic decision that the Habsburgs somehow managed to pass off as an administrative measure. The family had spent so much time marrying among themselves to maintain power that, by this point, the strategy seemed less a matter of discipline than of compulsion. 

Ferdinand and Isabella are remembered as the “Catholic Monarchs” who contributed to the unification of Spain, but they were also second cousins who married within the same noble network. Their union reshaped European history, while at the same time fitting into an older royal tradition that viewed family ties as an asset rather than a problem. 

Louis XIII of France married Anne of Austria as part of a union intended to stabilize relations between Bourbon France and Habsburg Spain, and the fact that they were close relatives was hardly considered remarkable. This is one of the recurring themes of royal history: diplomacy and consanguinity have consistently gone hand in hand, under the guise of prudence. 

George, then Prince of Wales and the future George IV, married Caroline of Brunswick, who was also his cousin, and their marriage soured from the very beginning. This serves as a useful reminder that while marriages between cousins might seem perfect on a family tree, they offered no guarantee of harmony once the union was sealed. 

Victoria and Albert are often remembered as a royal couple whose devotion to one another was extraordinary, which can make us forget that they were first cousins. Their marriage became a model for married life within the monarchy, but it also helped to illustrate just how common marriages between cousins still seemed to be among European royal families in the 19th century. 

Christian IX and Louise of Hesse-Kassel were close relatives who married within a dynastic context in which Danish succession policy and family ties were inextricably linked. This marriage was not only personal but also strategic: it combined claims to the throne, alliances, and an ancestral instinct to maintain legitimacy within the same extended clan. 

Philip III married Margaret of Austria, another marriage within the Habsburg family that contributed to the dynasty’s isolation from the outside world. The family was so determined to preserve its influence through intermarriage that a union like this was hardly considered an exception in the eyes of the court—which speaks volumes. 

Philip IV went even further and married Marianne of Austria, his own niece, after a previous marriage plan had fallen through. This is one of those cases where royal politics ceased to merely narrow the range of possibilities and instead moved directly toward something that, beyond any consideration of modern sensibilities, seems to have been orchestrated in a disturbing manner.

Louis XIV married Maria Theresa of Spain to seal the Peace of the Pyrenees, and this union brought together two people who were already closely related by blood. Royal propaganda loved to portray this kind of marriage as a triumph of the art of governance, even though, viewed from a distance, it often gives the impression that Europe was trying to resolve continental conflicts by always turning to the same handful of relatives. 

Ferdinand I and Marie-Caroline of Austria were another typical 18th-century couple resulting from a marriage between cousins, in which politics, inheritance, and family ties were intertwined in a single ceremony. Their union illustrates just how often royal houses viewed the idea of marrying outside their own circle as a true lack of courage.

When Ferdinand VII married Marie-Christine, he was marrying his niece, for it seems that the courts influenced by the Bourbons and the Habsburgs had never encountered a family circle—already small—that they could not make even smaller. This marriage was also of paramount importance for the line of succession, which meant that this delicate personal situation had national implications. 

Nicholas II and Alexandra Feodorovna were related through the dense web of European royal families—that same intertwined network that made marriages in the Empire’s final years seem less like new alliances and more like internal reshuffles. At that time, so many royal houses were linked to one another that family gatherings and geopolitics were beginning to overlap in a somewhat awkward way. 

The marriage of William II to Augusta Victoria also fit perfectly into this same European royal system, in which marriages between cousins were commonplace. When one has spent enough time studying these lineages, what at first seems exceptional eventually comes to appear as the standard way the monarchy operates: inheriting, negotiating, and marrying someone who is already on the list. 

Louis XVI and Marie Antoinette are generally portrayed as the product of a diplomatic alliance between the Bourbons and the Habsburgs—which they indeed were—but they also belonged to the same, closely intertwined ruling class. Even these marriages—remembered for their wigs, scandals, and the Revolution—were still rooted in the old belief that royal blood must circulate within a very exclusive circle. 

On the surface, Juan Carlos and Sofía projected the image of a decidedly modern 20th-century royal couple, but they, too, were bound by Europe’s well-known network of dynastic ties. This is part of what makes royal genealogy so strange: outfits become more modern, weddings are broadcast on television, but the lineages remain stubbornly old-fashioned. 

Queen Elizabeth II and Prince Philip were related through Queen Victoria, but also through the Danish royal line—a very effective way for members of royalty to be second cousins. Their marriage seems recent enough to appear ordinary, but it was nonetheless part of the long European tradition in which royal families have been intermarrying for generations. 

If there is one final dark chapter looming over all of this, it is the marriage of Philip IV and Maria Anna of Austria, as well as the birth of Charles II, whose health and succession issues became a warning that royal Europe could no longer ignore. At a certain point, the dynastic strategy ceased to resemble a judicious consolidation and began to take on the appearance of a biological debt that was coming due.