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Sarah Armstrong-Jones (later Lady Sarah Chatto), the daughter of Princess Margaret and the Earl of Snowdon, as chief bridesmaid at the wedding of Charles, Prince of Wales, and Lady Diana Spencer at St Paul's Cathedral, London, 29th July 1981. (Photo by Keystone/Hulton Archive/Getty Images)

Sarah Armstrong-Jones (later Lady Sarah Chatto), the daughter of Princess Margaret and the Earl of Snowdon, as chief bridesmaid at the wedding of Charles, Prince of Wales, and Lady Diana Spencer at St Paul's Cathedral, London, 29th July 1981.  (Photo by Keystone/Hulton Archive/Getty Images)

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GREAT BRITAIN - JULY 29: Diana, Princess of Wales and Prince Charles, Prince of Wales on their wedding day at St Paul's Cathedral, Sarah Armstrong-Jones is the bridesmaid behind them (Photo by Tim Graham Photo Library via Getty Images)

GREAT BRITAIN - JULY 29:  Diana, Princess of Wales and Prince Charles, Prince of Wales on their wedding day at St Paul's Cathedral, Sarah Armstrong-Jones is the bridesmaid behind them  (Photo by Tim Graham Photo Library via Getty Images)

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Lord Linley (foreground, left) as a pageboy with his sister, Lady Sarah Armstrong Jones as a bridesmaid, children of Princess Margaret and Anthony Armstrong-Jones, during a wedding at St Margaret's Church in London on 10th February 1969. This image is one of a series taken by Ray Bellisario who was credited with being the "original paparazzo" and someone who frequently upset the Royal Family with his informal and often unwelcome style of photography. (Photo by Ray Bellisario/Popperfoto via Getty Images/Getty Images)

Lord Linley (foreground, left) as a pageboy with his sister, Lady Sarah Armstrong Jones as a bridesmaid, children of Princess Margaret and Anthony Armstrong-Jones, during a wedding at St Margaret's Church in London on 10th February 1969. This image is one of a series taken by Ray Bellisario who was credited with being the "original paparazzo" and someone who frequently upset the Royal Family with his informal and often unwelcome style of photography.  (Photo by Ray Bellisario/Popperfoto via Getty Images/Getty Images)