You might have noticed so far that although the unlucky princesses have generally been unhappy in their marriages, none of them have specifically been murdered on the orders of their unpleasant spouse.

Step forward Blanche of Bourbon. 

One of the most famous losses to the English throne, Edward the Black Prince was extremely popular for most of his life, but ended it a sick, bitter man. 

Caroline Matilda was born into a court in mourning. Her father Frederick, Prince of Wales, had died four months earlier leaving his wife Princess Augusta a widow with nine children. The family had long been estranged from Frederick's father, King George II of England, but the Princes' death led to a cooling of tensions. Although George didn't like Augusta, and didn't like her reluctance to take part in court activities, she was generally left to raise her children as she saw fit. 

At his birth Eustace of Boulogne couldn't have hoped to become anything more than a nobleman, like his father and grandfather. He was due to inherit his mother's county of Boulogne, Stephen himself was a younger brother who had married the heiress Matilda of Boulogne, and had taken title Count of Boulogne through her. As the eldest son Eustace could look forward to becoming Count Eustace of Boulogne in the future. But in infancy he gained a new title and new future – Prince Eustace, heir to the English throne. 

If you want to look at an unhappy Royal family in history, then you don’t have to look much further than King Edward II and Queen Isabella. A marriage that was supposed to seal peace between England and France eventually led to a rebellion against the King. While their son Edward III certainly had a happy marriage, the same cannot be said for his two sisters. 

A potential King Arthur of England, young Arthur of Brittany was the son of Duke Geoffrey of Brittany and his wife Constance, and thus had Royal blood in his veins. Geoffrey was the son of King Henry II of England and Eleanor of Aquitaine, while Constance was descended from Scottish kings. Geoffrey died a few months before Arthur's birth, leaving Constance to protect both their son and the Duchy of Brittany. As the grandson of Henry II, baby Arthur was also a potential claimant to the English throne. 

If you don't get along with your mother-in-law then spare a thought for poor Maria Josepha of Bavaria. Not only did she get an overbearing mother-in-law in the form of Empress Maria Theresa, but she also had a husband who spent most of their marriage showing his complete disdain for her. 

 Henry Plantagenet is the only prince in the "Almost Kings" series that actually had a coronation. Known to history with the epithet "the Young King", Henry spent most of his short life feeling very hard-done by. 

Technically known to history as “Juana of Castile” (a name that would later be taken by one of her nieces), Juana la Beltraneja's more well-known name comes from the questions that surrounded her birth. Her mother Joan of Portugal was a Queen Consort of Castile as the second wife of King Enrique IV of Castile. Enrique had had his first marriage dissolved after thirteen years on the basis that it had never been consummated due to impotence (caused by a curse). 

If you consider that in the medieval period, the eldest son was the main heir to his father's estate, then you can't help but feel very sorry for poor Robert Curthose. As the eldest son of William, Duke of Normandy and Matilda of Flanders, he was already due to inherit Normandy in the future. In 1066 his father became King of England, and the teenage Robert would have been able to think of himself as the future King Robert I of England.