When he became Holy Roman Emperor in July 1658, Leopold I was already very familiar with how essential a spare to the heir was. 

Born in August 1198, Alexander II became King of Scotland at the age of 16. Two years later he attempted to take advantage of the chaos caused in England by the revolt against King John, but after John's death led to a change in English leadership the Scots were forced to return home. The Treaty of Kingston was signed in 1217, and in the following years diplomatic efforts led to the still unmarried Alexander being given the hand of the young English princess Joan.

King Manuel I of Portugal is known as “Manuel the Fortunate” because he wasn't supposed to become King. He was the youngest of his parents nine children and the last of their six sons, but illness and murder conspired to leave him as the sole heir to both his parents lands and the family's claim to the Portuguese throne.

King James V came into his inheritance at the tender age of 18 months, after his father died at the Battle of Flodden. His youth was spent with various Scottish Lords, including his stepfather, fighting out for custody and control of the young King. At the age of sixteen he managed to escape his stepfather and declared his minority over, although he still struggled against competing factions at his court.

This month's “Desperately Seeking Sons” candidate is King Baldwin I of Jerusalem.

Only the second King of Jerusalem, Baldwin was married three times during his life, and even courted controversy with his third marriage as his second wife was very much alive and very cross with how she had been treated. Historians have debated Baldwin's treatment of the women in his life, with some suggesting that he was homosexual (which may also explain why he doesn't appear to have fathered any children, legitimate or otherwise). But with so little information about his wives and their marriages, making a guess at his sexuality is difficult.

At the birth of Prince Louis of France some time during 1120 there was no guarantee that he would become King. He was the second son of King Louis VI, aka “Louis the Fat”. With an elder brother, Philip, who looked to be a relatively healthy child it was hoped that the “spare” would not be needed.

King Henry VIII is known for having six wives in his obsessive quest for legitimate male heirs. But Henry wasn't the only King in history to have this problem. While no one in Western Europe quite managed to top his total of six, there were a few kings that married multiple times before they got the desired heir, and occasionally a spare.

King Philip II of Spain was married a total of four times. His second marriage is quite well known in British history, as his wife was Queen Mary I of England. But before Mary and after her there were several women to whom he was married, and three of them were related to him, one way or another.

It's not often that an Almost Queen goes from the dizzying heights of a royal marriage, to plummeting down the social lists and marrying for love, but Cecily of York is one of a few exceptions to the rule!

This month we take another look at the Holy Roman Empire for our latest Almost Queen. The death of a sixteen year old Archduchess ultimately led to a marriage reshuffle that saw her youngest sister end up in France, raising the question of what might have happened had she survived.

When George William Frederick, Prince of Wales, became King George III of Great Britain in 1760, he instantly became the most eligible bachelor in Europe.

However the field of candidates was somewhat narrower than it had been for his medieval predecessors. There could no longer be a glorious match with a wealthy French princess or a well-connected Spanish infanta, because the bride had to be a Protestant. As a result George was confined to looking to Scandinavian candidates, and the young women of the German principalities.