Born on 5 August 1103 William Adelin would have been the first Anglo-Norman King, reflecting the changes in English society since the Conquest. While his father was King Henry I of England, the youngest son of William the Conqueror, his mother was Matilda (formerly Edith) of Scotland. Her mother had been a granddaughter of the old Anglo-Saxon kings, and had married King Malcolm III of Scotland in 1070. William Adelin might even have had a claim on the Scottish throne if he had survived. 

Although her early life can classify her as an “Unlucky Princess”, in many ways Margaret of Austria’s life was better than other such royal women. Betrothed and married several times, she was not only eventually allowed to manage her own destiny, but she became ruler of the Netherlands as Regent for her nephew. Through this she joined the ranks of other strong women who managed the region on behalf of their menfolk. 

Unless he thought about changing his name, as later Kings did on accession, then Britain could have had it's first King Fred in the 18th century. On his birth in 1707 the idea that the Electors of Hanover would become Kings of Great Britain was becoming more obvious. Queen Anne had no surviving children, and Frederick's great-grandmother Sophia was Anne's nearest Protestant relative. 

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.