Sophia Dorothea of Celle (or Zell) was the only acknowledged wife of King George I of England, while he was still just ruling Hannover.
It was a marriage born in money and power. She was the only heir of her father (his uncle), the Duke of Brunswick-Luneburg (Braunschweig-Lueneburg), and his Huguenot mistress/morganatic wife/eventual full wife, Eleonore d’Esmier d’Ombreuse, Countess of Wilhelmsburg. As heiress, she came with an income of 100,000 thalers a year, but she couldn’t inherit the duchy because that went with the male line. She was also George’s first cousin, but we all know that European aristocrats of that era weren’t bothered by that sort of genetic stupidity. George was going to inherit Celle eventually, but the marriage would lead up more gracefully to unification. (In theory.)
However, there was a lot of soap opera involved. Even though it was a sensible marriage idea (from the point of view of eliminating dynastic contention), the Hannover side jibbed at marrying George to the daughter of a morganatic marriage.
But why was the marriage initially morganatic? Because in 1658, as part of a deal to get out of marrying Princess Sophia of the Palatinate, when he gave Hannover and the obligation to his younger brother, Ernest Augustus of Brunswick-Luneburg (who was happy to marry Sophia and vice versa, and who thus became the father of George I), he had promised to remain unmarried and produce no legitimate heir. He initially kept his promise. Then he met Eleonore in 1665 and fell in love with her. They married morganatically, and Sophia Dorothea was born in 1666. Ten years later, it was becoming clear that the future George I was the only male heir born to the whole extended family, so Sophia Dorothea’s dad proposed the marriage idea and got turned down. This torqued him off, so he broke his promise, married Eleonore, and legitimized Sophia Dorothea in 1676.
This made the relatives angry, but it also got the job done. Sophia Dorothea became Duchess of Hannover, but there wasn’t much fun in it.
She bore two children: the eventual King George II of England and the eventual Queen Sophia Dorothea of Prussia.
In 1692, after ten years of marriage and much abuse by her husband, there was a scandal about her friendship with a Swedish count, Philip Christoph von Koenigsmarck. The Duchess protested her innocence. In 1694, Koenigmarck disappeared mysteriously; rumor said he had been murdered. The duke divorced and imprisoned Sophia, but he didn’t divorce his claim to inherit his uncle her father’s duchy, which he collected in 1705 when that duke died.
[It was rumored that the whole thing had been engineered by George’s long-time mistress, Ehrengard Melusine von Schulenburg. She was also rumored to have been made his morganatic wife, but George never acknowledged this in public and never acknowledged his illegitimate kids as legitimate heirs. (This did protect the claim of his “heir and spare” kids and prevent potential dynastic warfare, which is probably why he did it.) However, he did give Melusine tons of properties and noble titles, including making her “Duchess of Kendal” (her usual title in English history books) and “Duchess of Munster” (which was a real insult to the Irish). In Scottish history, she is best remembered by the reference in the Jacobite song “Cam’ Ye O’er frae France” to George “riding on a goosie.”]
So anyway, the upshot was that this lady was deprived of her freedom, her property, visits from her kids (even after they grew up), and the ability to marry again. She lived that way for thirty years. Contemporary accounts say that she never ceased to declare her innocence of all adultery or immoral behavior.
Her son planned to free her and clear her name as soon as he acceded to the throne, but unfortunately she predeceased his father. It’s a sad story.
(To add to the creepiness of George I’s court, he had so many mistresses that most of the English nobles mistook his semi-acknowledged illegitimate half-sister, Sophia von Kielsmansegg, for one of his mistresses – just because she was influential with him! Apparently people didn’t get the word about the real relationship until he made her Countess of Leinster, gave her arms featuring a bar sinister, and talked about their “common blood” in the letters patent for the title. And yeah, I’m sure that the Irish were just super-pleased by the insult to Leinster, too.)
* Morganatic marriage, aka “left hand marriage,” was part of ancient Frankish law but went against Church and international law. It was a form of marriage between two people of unequal status, signified by the giving of a “morning gift” after the consummation of the “marriage.” No dowry or brideprice was given, and the families of the people involved did not get into negotiating a marriage contract. A morganatic marriage could be ended unilaterally at any time. (And they often were, if a lord got a full marriage prospect that paid off better.) But it was still one step above being a mistress, and there was only supposed to be one morganatic marriage at a time. But since they were enacted in private and not in church, morganatic marriages could potentially make morganatic bigamy pretty easy.
Under Frankish law, the children of an unequal marriage were still automatically heirs of their fathers, but this was not true under German or international law. (Although a lot of the resulting kids were legitimized by their fathers, a lot of them weren’t.) In the eyes of Catholic and Protestant churches, this form of “marriage” was keeping a concubine. The closest English equivalent would be “common law marriage,” not that such a thing exists anymore.
As time went on, German and Austrian law did begin to recognize morganatic marriages as merely a specialized form of pre-nuptial agreement that controlled the succession of heirs to titles, without de-legitimizing children or making divorce easy. This allowed them to be recognized as true marriages by churches, and some of these later morganatic marriages did take place in churches, before consummation, instead of in bedrooms.
One notable latter-day morganatic marriage was the marriage of Archduke Franz Ferdinand, heir to the Austro-Hungarian Empire, to Countess Sophie Chotek, a Hungarian noblewoman of high birth. Because of their unequal (though high) rank, their marriage was severely opposed by Emperor Franz Josef. After most of the crowned heads of Europe and the Pope interceded for the couple, the Emperor finally acceded, but only under the condition that it be a morganatic marriage where Sophie would never become empress and the children could not succeed to any titles.
The Emperor refused to attend or let most of the relations attend, so the Nuptial Mass was celebrated in the tiny Reichstadt Castle chapel. But the celebrants were the parish priest with two friars as deacon and subdeacon; so the Mass itself was in full splendor, and showed that the Church regarded it as a true marriage of equals.
Here’s a picture from an illustrated journal of the day, The Sphere. (Also note that the Catholic archduchesses all wore hats to Mass.)

Caption: “THE WEDDING OF THE ARCHDUKE FRANZ FERDINAND AND THE COUNTESS SOPHIE CHOTEK AT REICHSTADT.”
“The Archduke Franz Ferdinand duly wedded the Countess Sophie Chotek, the choice of his heart, at the Imperial castle of Reichstadt in Bohemia last Sunday week. The service was conducted by the parish priest, assisted by two Capuchin friars The little wedding procession, consisting of thirty-one persons, proceeded from the Archduchess Maria Theresa’s drawing room through the billiard room, where the Emperor Franz Josef and the Czar Alexander II met in conference in 1876, to the little chapel, to which no one else was admitted. First in the procession walked the bridegroom with his stepmother the Archduchess Maria Theresa, and his two half-sisters, the Archduchesses Maria Immaculata and Elizabeth, and his two sisters; and after then the bride, accompanied by her uncle, Prince Löwenstein, and Count Charles Chotek, head of the family. The Countess wore a white silk dress trimmed with myrtle blossoms, and on her forehead a diamond coronet, a wedding gift from the Archduke. Behind her came her brother, her sisters, and their husbands, and two or three court dignitaries. The Archduke Franz Ferdinand’s brothers were not present. From Reichstadt the bride and bridegroom proceeded to Konopischt Castle in Bohemia, a favourite estate of the Archduke’s, where they are passing their honeymoon. Our picture is by the one artist present (a Viennese).”