Yet, behind the scenes of the 1981 wedding - which took place 37 years ago tomorrow - the late royal had been left “in tears” by the discovery that the first-in-line to the throne was still in love with Camilla Parker Bowles.
Diana, then just 20 years old, had seen her waist shrink by more than five inches in just four months, according to the designer of the iconic dress she wore down the aisle at St Paul’s Cathedral in London.
Speaking in a new Channel 5 documentary - Charles and Di: The Truth Behind Their Wedding - which aired last night, designer Elizabeth Emmanuel told how the stunning white dress had to be altered several times to fit Diana’s increasingly small frame.
“She did lose weight, she was losing so much, we even had to start again a couple of times, even after cutting into the fabric," she explained, of the story behind the gown which she co-created with ex-husband David.
“Her waist was a size 23 at the end. She was tiny like a model.”
The dress for what was billed as a “fairytale wedding” went on to spark a number of bridal trends.
In the days leading up to the wedding, Diana - who passed away in 1997 - discovered a package with Camilla’s name on it.
It contained a bracelet from Charles, then 32, for the woman who would become his second wife.
“She was absolutely in tears, in a terrible state about it. And it was clear that it was Prince Charles’ farewell present to Camilla,” explained Christopher Wilson, a royal expert, on the programme.