As she stepped into the Royal Opera House for a concert marking one of the biggest political events of her reign, Elizabeth II was the picture of serenity. But just minutes earlier she had had to perform a tiara swap as her jewels fell apart in the back of her royal car.

Queen Elizabeth II was on her way to attend the Fanfare for Europe gala in central London on January 3rd 1973 when the incident happened. The concert was a showpiece event to mark the United Kingdom’s entry into the European Economic Community (later the European Union) and this royal extravaganza was to be a crowning moment in this major change to the political landscape.

Edward Gregson had composed a special fanfare while the UK’s Prime Minister, Edward Heath, was on hand to accompany The Queen and the Duke of Edinburgh into the Royal Opera House for the evening show. But as her car swept from Buckingham Palace to Covent Garden, Her Majesty noticed something was wrong. Her tiara had broken and was unusable for the evening ahead. Yet when she stepped out of her car soon afterwards, she was wearing a sparkling diamond diadem and smiling as if nothing had happened.

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The tiara disaster had been solved by one of her courtiers and friends, Lord Plunket. There was no time for the royal party to swing back to the Palace and pick up another set of gems. However, Lord Plunket’s London home was en route to Covent Garden and he was quickly dispatched to retrieve his family’s own tiara. Whether Queen Elizabeth II swapped diadems in the back of the car or in a discreet space away from the cameras isn’t known. But she made her entrance to the gala, on time and every bit as sparkling as was expected for this major event in her reign.

The evening itself attracted some dissent with small protests outside the Opera House. However, once inside Queen Elizabeth II settled down to an evening of music to mark a milestone in her reign, glittering as usual but this time, in borrowed diamonds.

Lydia Starbuck is a pen name of June Woolerton who has written extensively on royal history. Her book, A History of Royal Jubilees, is available now. She is also the author of a popular cosy mystery, All Manner of Murder.