The late Princess Diana felt her relationship with the Prince of Wales started to get "serious" when she was a teenager.

Princess Diana

Princess Diana

The blonde royal - who tragically passed away in 1997 - has admitted she felt her romance with Prince Charles started to blossom two years prior to their wedding day in 1981 when she was "18 and a half" years old.

Speaking in an upcoming documentary titled 'Diana - Her Story', she said: "When the [relationship] really started to get serious ... I must have been 18 and a half. I was asked to stay with some friends in Sussex, and they said, 'Oh, the Prince of Wales is staying the night because he's playing polo.' So I thought, 'Well, I haven't seen him for ages, he's just broken up with his girlfriend; [his great-uncle Lord] Mountbatten's just been killed. And I said it will be nice to see him."

But the Sussex encounter was not the first time the pair had met, as Charles has previously dated Diana's older sibling Lady Sarah.

And Diana, who crossed paths with the 68-year-old royal in 1977, felt "quite impressed" by their following meetings.

She said: "I thought, 'I am quite impressed this time around.'"

Meanwhile, Diana - who has Prince William, 35, and Prince Harry, 32, - has revealed one of her happiest times in her life was living in a flat in London's Old Brompton Road.

She said: "I was so happy there. I had three girls living with me. I had the best time of my life."

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