How the royals have changed: Why Harry couldn't have wed Meghan in the past

Today is a joyous occasion for the royal family, as Prince Harry, fifth in line to the throne, announces he will marry Meghan Markle.

But just a few decades ago a union between a British royal and an American divorcee was unthinkable.

In 1936 the royal family almost imploded when King Edward Vlll chose to marry the twice-divorced American socialite, Wallis Simpson.

King Edward VIII became the first British king to abdicate the throne for his American divorcee bride Wallace Warfield Simpson. The two stand at Chateau de Cande where they were married in France in 1936. Photo / Getty Images

As the monarchy ruled over the Church of England, which would not condone divorce or remarriage, the King was forced to abdicate to his brother King George Vl.

Only two decades later King George Vl's daughter, Princess Margaret, was told she would have to "renounce her rights to succession" if she chose to marry divorced man Peter Townsend.

So instead she wed British photographer and film maker Antony Armstrong-Jones, better known as Lord Snowden.

Princess Margaret and Antony Armstrong-Jones leaving Westminster Abbey on their wedding day in 1960. Photo / Getty Images

So while Margaret had to give up on Townsend, fast-foward a couple of decades and attitudes towards royal marriage and divorce had changed dramatically.

A fairy tale wedding in 1981 saw Prince Charles marry Lady Diana Spencer in front of a global television audience of 700 million people.

The Prince and Princess of Wales on the balcony of Buckingham Palace on their wedding day, 29th July 1981. Photo / Getty Images

But after very public marriage troubles and affairs on both sides the couple divorced - by order from the Queen - in 1996. The following year Diana was tragically killed in a car accident.

Charles went on to marry his long-time lover Camilla after her marriage ended, forming a union from two divorced parties.

While the marriage was allowed, neither Queen Elizabeth or Prince Philip attended the ceremony.

Charles, the Prince of Wales, and his new bride Camilla, Duchess of Cornwall, in the White Drawing Room at Windsor Castle on April 9, 2005. Photo / Getty Images

And after Prince William married Kate Middleton in 2011, the monarchy saw one of the biggest changes in British royal succession law to date.

The first child born to the Duke and Duchess, whether boy or girl, would be next in line to the throne after their father.

Kate and William on their wedding day six years ago. Photo / Getty Images