It’s been 44 years since Princess Diana and now-King Charles III exchanged vows in what became one of the most-watched royal weddings in history.

The couple were married on Wednesday, July 29, 1981, at St. Paul’s Cathedral in London. Diana was just 20 years old at the time, while Charles was 32.

An estimated 750 million viewers across 74 countries tuned in to witness the royal ceremony. During the service, Diana made a bold choice in her vows, choosing to leave out the traditional promise to “obey” her husband. Instead, she pledged to “love him, comfort him, honour and keep him, in sickness and in health.”

According to The New York Times, Diana and Charles had “very serious” conversations ahead of time about whether or not to include the word “obey,” ultimately deciding to leave it out.

A Slip of the Tongue at the Altar

Nerves were high during the ceremony, and one small mistake by Diana made headlines. While reciting her vows, she accidentally got Charles’ name wrong, calling him “Philip Charles Arthur George” instead of the correct “Charles Philip.”

This slip was noted in royal biographer Sally Beddell Smith’s book Prince Charles: The Passions and Paradoxes of an Improbable Life, and was also reported by the BBC at the time: “Wedding day nerves were apparent during the ceremony. Diana mixed up the Prince’s names, calling him Philip Charles Arthur George, rather than Charles Philip.”

Charles also had a small blunder of his own, saying “thy goods” rather than “my worldly goods.”

Diana’s Personal Letter Reveals Her Emotions

A recently resurfaced letter from Diana has shed more light on her feelings just days after the wedding. The letter, written on July 31 — two days after the ceremony — was addressed to Mark Simpson, a footman at Buckingham Palace. It was obtained by PEOPLE and made public via Julien’s Auctions on May 30.

In it, Diana thanked Simpson for his support during her early days in the palace:
“I just wanted to thank you for all your kindness + patience you’ve showed towards me since I moved into B.P. My stay was made so much easier by your company as it was so terribly lonely + we had so many laughs for that I can’t thank you enough.”

Feelings of Isolation Inside the Palace

There were long-standing reports that Diana felt isolated and unsupported within the royal household. In later interviews, she admitted to experiencing deep loneliness and depression during her early years in the palace.

In her letter, she added a lighthearted note about the wedding day and her upcoming plans:
“Do hope you were able to enjoy Wednesday + that you liked my dress? I’m off to Britainia tomorrow, what with all those men around. I will have to keep a watchful eye on Evelyn!”

A Marriage Remembered

If they had remained together, Diana and Charles would be marking their 44th wedding anniversary today. However, the couple separated in 1992 and officially divorced in August 1996. Just a year later, in August 1997, Diana died in a car crash in Paris at the age of 36.