There's a reason her wedding to Prince Charles remains the most-watched royal wedding in history.

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Looking back on this day in royal history.

It's hard to believe that it's been almost 40 years since Princess Diana married Prince Charles, but here we are: July 29 marks 38 years since the day of one of the biggest royal weddings in history.

And while Meghan Markle and Prince Harry have practically taken on the mantle of "breakers of royal tradition," Princess Diana may have paved the way for them when she broke royal precedent during her wedding. According to a New York Times article from 1981, Diana was the first royal to omit the word "obey" from her wedding vows.

"In a break with royal precedent, Lady Diana Spencer has decided that she will not promise, at her wedding four weeks from today, to obey Prince Charles," the Times reported.

On This Day in History: Princess Diana's Royal Wedding
Credit: Princess Diana Archive/Getty Images

Following in her lead, Prince William and Kate Middleton also omitted the word from their vows, as did Prince Harry and Meghan Markle.

Though the weeks before the big event were marked with drama and media scrutiny for the soon-to-be Princess, the night before her wedding, 20-year-old Diana was reportedly heard singing, "I'm going to marry the Prince of Wales tomorrow!" while riding a bicycle in circles at Clarence House.

How Princess Diana Broke Royal Tradition on Her Wedding Day
Credit: Princess Diana Archive/Getty Images

On the day of, Diana had a beauty disaster that almost ruined her wedding dress, but like a true graceful princess, she made lemonade out of lemons. She reportedly went to give herself one last spritz of Houbigant Paris Quelques Fleurs ($240;, but the lid of the bottle came loose and spilled on her wedding dress. The perfume left a stain, but Diana made do by holding her dress up by the stained area so that it just looked as if she was lifting it up to avoid stepping on the hem.

Princes Diana Wedding Day Charles and Camilla King and Queen in Waiting
Credit: Anwar Hussein/Getty Images

With 750 million viewers watching the wedding from home across the globe, Diana and Charles's wedding still remains the most-watched royal wedding in history.