Princess Diana's sister Lady Sarah Spencer secretly dated Prince Charles, the same year Diana would meet her future husband.
In 1977, Prince Charles was facing mounting pressure from the royal family to find a suitable wife.
Charles met Lady Sarah Spencer, and the two enjoyed a whirlwind romance where the royal even took her to lavish ski resort Klosters, Express claims.
Although very little detail is known about the relationship, Charles reportedly ended the romance when he spotted Sarah speaking to a journalist.
James Whittaker, a journalist at the Mirror, says: 'Sarah was disarmingly frank about her boyfriend and declared she would not marry Charles ‘if he were the dustman or the King of England’.'
'That was good news from where I was sitting and Sarah seemed delighted I was so keen to share it with the nation,' Whitaker said.
Following the end of their relationship, Charles sparked up a romance with Sarah's younger sister - the late Lady Diana Spencer.
However, despite their history Sarah not only gave Charles and Diana her blessing, she also set them up on their first date, telling The Guardian in a later interview: 'I set them up, I'm cupid.'
Four years later in 1981, Diana became the Princess of Wales after tying the knot with the royal in a world-famous ceremony while Lady Sarah wed Neil McCorquodale.