Prince Harry is engaged to American Meghan Markle

King Edward VIII sacrificed his throne and Queen Elizabeth's sister Margaret gave up her one true love, but for Prince Harry marrying a divorcée is no longer a bar to being a royal or following his heart.

On Monday, Harry, fifth-in-line to the British throne, announced he was to wed his girlfriend, divorced US actress Meghan Markle, with the blessing of his grandmother, the queen.

British social attitudes have been transformed in recent decades but the monarchy has been bound by a more traditional set of Christian values.

So the queen's approval is a stark demonstration of how much the monarchy has also changed and modernized in the past 80 years when the idea of a royal marrying someone who was divorced was inconceivable.

"It's extraordinary how far we've come since the 1930s," said royal biographer Claudia Joseph. "In less than a century times have changed beyond all recognition."

Famously, Harry's great-great-uncle Edward VIII set off a constitutional crisis in 1936 by insisting on marrying twice-divorced American socialite Wallis Simpson to the horror of the British establishment, the government, and the Church of England, which the monarch nominally heads.

It was dubbed "the greatest love story of the 20th century" and Edward abdicated after just 11 months on the throne and ended up living in France, meaning Elizabeth's father George VI unexpectedly became king.

"You must believe me when I tell you that I have found it impossible to carry the heavy burden of responsibility and to discharge my duties as king as I would wish to do without the help and support of the woman I love," Edward said in his abdication speech.

Such attitudes were still prevalent two decades later. In 1955, Elizabeth's younger glamorous sister Margaret was forced to call off her proposed marriage to a dashing air force officer, Group Captain Peter Townsend.

Although a royal equerry, Mr. Townsend was still deemed an unsuitable husband for the queen's sister because he was divorced and he was sent off to Brussels by Buckingham Palace.

"I would like it to be known that I have decided not to marry Group Captain Peter Townsend," Margaret said in a sad announcement to the nation. "Mindful that Christian marriage is indissoluble and conscious of my duty to the Commonwealth, I have resolved to put these considerations before others."

While divorce was considered unfathomable in those days, it has since become a common feature for the Windsors. Of Elizabeth's four children, three of their marriages have ended in divorce, most spectacularly that of Harry's father, heir-to-the-throne Charles, Prince of Wales, and his first wife Diana.

They divorced in 1996, 15 years after their fairytale wedding and a year before she was killed in a car crash in Paris and Charles went on to wed another divorcée Camilla Parker Bowles in 2005.

Camilla was someone who he had first considered marrying in the early 1970s but who royal courtiers had considered unacceptable while she was not keen on taking on the role herself at the time.

However Charles and Camilla could not marry in church, and the queen, who holds strong religious beliefs and has taken her role as Supreme Governor of the Church of England very seriously, declined to attend the civil ceremony.

The Church of England had only ruled three years earlier that a divorced person could "in exceptional circumstances" marry again in church while their former spouse was still alive.

Ms. Joseph said Charles's second marriage had paved the way for Harry.

"I think the dilemma came when Prince Charles married the Duchess of Cornwall," she told Reuters. "That was a hard thing for the queen to deal with. Somehow they had to marry without compromising her role as head of the church."

Harry and Meghan's union, like all those of the first six royals in direct line of succession, must be approved by the queen under the 2013 Succession to the Crown Act, which replaced an even more prescriptive law dating back to the 18th century.

"The Queen and The Duke of Edinburgh are delighted for the couple and wish them every happiness," Buckingham Palace said in a statement.

This story was reported by Reuters.