On the wedding day, King Charles assured Princess Diana, 'I'll be there for you'

The night before their wedding, King Charles sent a special letter to Princess Diana.

The couple's 1981 wedding was one of the most popular royal family weddings.

While their parents planned the marriage, the King made care to send his future wife a personal message ahead of the big day, expressing his love for her.

"The night before the wedding, which Diana spent at Clarence House with her sister Jane," royal biographer Penny Junor recounts, "he sent her a note, along with a signet ring that bore the Prince of Wales feathers."

'I'm extremely proud of you, and when you come up, I'll be there at the altar for you tomorrow,' the King said in his letter. Just stare 'em in the eyes and knock 'em out.'"

After a troubled marriage and two children, King Charles and Diana divorced in 1992. In 2005, His Majesty married Queen Camilla.