If you're the king, your private life becomes public knowledge. In an earlier post I discussed some well-known royal divorce cases from medieval Europe. Here I discuss two more.
One of the most significant for political history was the divorce of Louis VII of France and Eleanor of Aquitaine in the 1150s. He was the heir to the French throne and she the heiress to the duchy of Aquitaine, essentially the southwest quarter of France, a very wealthy territory, so it seemed like an excellent match when they married back in 1137. But they were related within the "forbidden degrees," being third cousins. When after years of marriage they had only had a couple of daughters, Louis became convinced they were being punished by God for the sin of incest. After all, one of the main duties of a king is to have a son to keep the line going.
They went on the Second Crusade together as penance, but the Crusade was a disaster. On the way home, they stopped in Rome, where the pope formally forgave them for their "incest" and promised them a son. The next year they had another daughter.
So Louis got the French bishops to annul their marriage (the pope was furious when he found out) and quickly married again. He did eventually have a son, the future Philip II. He seems to have expected Eleanor to retreat to a life of seclusion and contemplation.
Instead she too remarried. Initially, on the way back to Aquitaine from Paris, she was pursued by half the unmarried nobles of France--and some of the married ones. But she managed to outride them (think of the scene with Arwen and the Black Riders in the first "Lord of the Rings" movie). But it was obvious she would only be safe if married. She chose Henry, the young heir to Normandy and Anjou in western France, soon to become Henry II of England. They went on to have five sons (and a couple of daughters), suggesting the failure of Louis and Eleanor to have sons was not her fault.
Politically, Aquitaine now was attached to the English crown, not the French one--an issue that caused tension throughout the rest of the Middle Ages, culminating in the Hundred Years War. Interestingly, the new spouses Eleanor and Louis married after their divorce were also their third cousins.
Louis's son and heir, King Philip II of France, also had a messy divorce. He went on the Third Crusade in 1189, got sick (perhaps malaria, there were lots of diseases in the Near East unknown in western Europe), and went home. Shortly thereafter he married Ingeborg of Denmark, who actually was not his cousin. But on their wedding night he took an inexplicable dislike to her, perhaps related to his recent illness.
In the morning he declared they had not consummated their union and that the marriage should therefore be annulled. Ingeborg, on the other hand, said that they had in fact performed the "copula carnalis" (on which click here), that she had been right there, it was not the sort of thing a girl was likely to be mistaken about. The pope backed her up, but Philip refused to recognize her as his wife. It took years, and France put under interdict, before they finally reached an amicable agreement and Philip married a different woman, who gave him a son. This divorce case indicates the very strong medieval sense that marriage ought to be insoluble.
Interestingly, the church's emphasis from here on was on the permanence of marriage. To avoid quite so many divorces like Louis's and Eleanor's, the number of "forbidden degrees" was reduced from 7 to 4 in 1214, meaning anyone related more distantly than third cousins could not claim divorce on the basis of incest.