Princess Diana broke protocol for first time at 'horrendous' event with Prince Charles

Diana, who was 19 years old, chose a “sensational black dress” to attend a party at the Royal Opera House, in London.

It is believed that “the Palace did not know about the dress she chose,” the experts at A Royal Guide To… Fashion revealed.

The stunning gown broke the royal protocol in many ways, including its design as it was an off-the-shoulder dress.

Also, “it was black… when the Royal Family don’t wear black unless they are mourning,” they explained.

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source: express.co.uk