First Hollywood brought Grace and Rainier of Monaco together. Then the studios helped create THAT diamond engagement ring – the most famous and dramatic of them all!

The great 1950s romance of Grace Kelly and Prince Rainier of Monaco has a fitting sense of drama to it.

But so does the story of her jewellery – and how, in particular, she came to wear that 10-carat diamond sparkler on her fourth finger, a ring copied by stars down the decades.

It’s perhaps no surprise that Hollywood played a big part in introducing Grace to the Prince of Monaco. She was, after all, one of the most glamorous leading ladies of her era – perhaps any era.

Grace Kelly already had an association with Cote d’Azur yhanks to her starring role in Hitchcock’s 1954 To Catch a Thief, a caper set on the French Riviera.

Grace Kelly in High Society, her final film before she became Princess Grace. The huge engagement ring is real – and hers!

Prince Rainie and Grace, pictured at her parents’ home in Philadelphia after the announcement of the engagement in January, 1956

Grace pictured at the 1955 Cannes Film Festival, where she first met Rainier. Here she is talking to a peddler on the sea front

By the following year, she was an Oscar winner for her role in Country Girl. Then, in spring 1955 she found herself invited back to the Riviera for the Cannes Film Festival.

It was while travelling there on the luxury sleeper ‘Le Train Bleu’ that Grace happened to meet Olivia de Havilland – Gone with the Wind’s Melanie and a film beauty from an earlier generation – and husband, Pierre Galante. 

And it was there on Le Train Blue that Galante, an editor at Paris Match magazine, had a brainwave: he proposed an article and photoshoot with Grace and Prince Rainier of Monaco –  another figure of huge glamour, if in a different way.

Grace Kelly agreed, perhaps because she had become entranced by the gardens of the Palais de Monaco that she had spotted from the principality’s port the year before. That, at least, is the account given to Paris Match by her son Prince Albert in 2022

Rainer agreed, too. But on the afternoon of 6th May, at the appointed time, the Monégasque prince kept the Hollywood princess waiting for more an hour and so at their first meeting, she was more than slightly frosty.

She had to be back in Cannes for a festival cocktail party.

Once they stepped outside into the beautiful gardens that she had previously so admired, however, both sides relaxed.

She wrote him a thank you card following the visit and they continued to correspond through transatlantic phone calls and by post.

And so it was that, seven months later during the Christmas holidays of 1955, Prince Rainier crossed the Atlantic to meet Mr and Mrs Kelly, and propose to their daughter.

Yet  the ring he chose to take with him was not the one you might recognise – enormous, and repeatedly replicated (by Amal Clooney and Beyonce for example) 10-plus carat emerald cut diamond ring we have seen in countless photographs.

Photographs from the engagement announcement on January 5th 1956, show her wearing something rather different: a Cartier eternity ring set with alternating diamonds and rubies, purposely representing the colours of the principality’s proud flag.

And that, if you will excuse the pun, is when Hollywood lent another hand.

Grace Kelly on the set of To Catch a Thief, the 1954 Hitchcock film which had first brought her to the Cote d’Azur

The film poster for To Catch a Thief, a Riviera caper with Grace Kelly opposite Cary Grant

Grace wears a white strapless dress in a publicity shot for To Catch a Thief

It was just a few weeks later that Grace started filming her final pre-marriage movie, High Society, the story of Tracy Lord, a wealthy socialite engaged to be married, but in conflict with two other suitors – a photographer and an ex (Bring Crosby).

On the third day of filming, the costume department provided the world’s most famous fiancée with a huge ‘diamond’ ring. Grace took one look at the paste and asked if she might perhaps wear her own!

‘Well,’ said the director Charles Walters, ‘I will need to see it first to make sure it is good enough.’ His tongue was firmly in his cheek.

He would have seen pictures of Grace’s ring just a few weeks before and would have known that, although very pretty, it was neither accurate nor appropriate for a spoilt ‘high society’ girl from Philadelphia.

Prince Rainier had a more decisive response. 

On learning of the ‘fake’ and Grace’s request, he bought her another ring, this time more ostentatious, set with a 10.48 carat emerald-cut diamond, flanked by two baguette-cuts. 

‘Who, particularly a future princess, would ever dream of wearing paste, when a natural diamond will always out-sparkle any imposter?’ agrees Sam Broekema of the Natural Diamond Council.

Still a byword for glamour, Princess Grace arrives to compere a 1970 charity concert at the Royal Festival Hall 

Princess Grace’s giant diamond ring has had many admirers – and quite a few have followed the style , including Amal Clooney pictured here with fiance George in 2014

According to Robert Lacey in his biography Grace: Her Lives, Her Loves, Celeste Holm who played Liz Imbrie the journalist in the movie, said: ‘she came in with this diamond as big as a skating rink. It was beautiful, just beautiful! So full of life and sparkle.’

Other cast and crew members exclaimed with oohs and ahhs at the enormous diamond ring. (Like her first ring, it had been created by Cartier.)

Grace’s response was to rouge a little and reply: ‘Yes, it is sweet, isn’t it?’

‘We never let her forget it, we teased her about it until the last day of filming: Grace’s “sweet’ diamond” ring.’ Holm remembered.

I doubt she cared.

• Josie Goodbody, is a jewellery historian and author of mystery novels