Everyone knows the ring. A 10.48-carat emerald-cut diamond, two baguette stones on the sides, worth around four million dollars in the money of the day - over thirty-eight million today. What almost nobody knows is that it was not the first ring. It was the second.

When Prince Rainier III travelled to Philadelphia at Christmas 1955 to ask for Grace Kelly's hand, he carried a modest band with him. Made by Cartier, with diamonds and rubies, fashioned from two family jewels reworked into one. Red and white - the colours of the Monegasque flag. A ring that tells the future wife which country she will be living in.

Symbolism that is anything but small. And yet, according to sources close to that period, the prince considered the ring temporary - something like a promise, not enough for a woman who would be standing beside Hollywood stars of her rank.

What changed his mind was not conscience but a film scene. After the engagement was announced, Grace was shooting her last film, „High Society\". Her character was supposed to wear an engagement ring - and the production planned to use a prop. When the prince learned his fiancée would be wearing a fake ring on camera, he ordered a real one.

That is how the second ring came about, again from Cartier, and it is the one that appears in the film. Grace then wore it for the rest of her life. The three stones, according to the interpretation the family maintains, represent the past, present and future of their relationship.

That design still exerts influence today. Elizabeth Taylor, Beyoncé, Amal Clooney and Anne Hathaway have worn rings that recall it directly. That is a rare thing in fashion - an object from 1956 still dictating what brides will ask for in a jeweller's shop seventy years later.

After Grace's death in 1982, both rings remained with the Grimaldi family, where they are to this day. But only one entered history. The one made from family stones, in the colours of the country she went to live in, was forgotten the moment the bigger diamond arrived.

That is the story worth more than the carats. Not that the prince did not love her enough - but that he judged the personal, smaller, more thoughtful gift insufficient in front of the cameras. The ring made for her was replaced by a ring made for other people to see. That reflex is not monarchical and it is not Hollywood. That reflex is known to anyone who has organised a wedding.