Last November, Prince Harry shared his plans to marry American actress Meghan Markle with the public, but it wasn't until March 15, 2018 that their engagement became "official." That's when Queen Elizabeth II released a statement giving her formal consent for the couple to wed. Without it, their marriage would have been considered invalid under a British law that dates back to the 18th century.

According to Town & Country, the 1772 Royal Marriages Act stated that all marriages to a member of the British royal family were subject to the approval of the reigning monarch. The statute [PDF] read: "... every marriage, or matrimonial contract, of any such descendant, without such consent first had and obtained, shall be null and void to all intents and purposes whatsoever."

This rule received an update in 2013 with the passing of the Succession to the Crown Act. Today, only the first six royals in line to the throne require the monarch's permission to validate their marriages. That means that for Prince Harry—who was fifth in line when he announced his engagement, but knocked into sixth place in April with the birth of His Royal Highness Prince Louis of Cambridge—getting Granny's blessing was vital. Meanwhile, Harry's cousin Princess Eugenie (who's ninth in line) will be free to get married this fall with or without a thumbs-up from the Queen.

The Succession to the Crown Act became relevant late last month when Prince William and Kate Middleton welcomed baby Prince Louis into their family. Under the old laws, the birth of a boy would have bumped Princess Charlotte down a peg in the line of succession, but thanks to the new act she's the first female royal to maintain her spot over a younger male sibling.

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