Had Diana Spencer not crossed paths with Prince Charles in 1980, the world might never have fallen in love with the soft-spoken kindergarten teacher born to British nobility. And in the upcoming PBS special Diana - Her Story, producers uncover rare video of Diana telling the unlikely story of how she—a shy, unassuming teenager—caught the eye of Queen Elizabeth’s eldest son Prince Charles, forever changing her fate from private teacher to public figurehead.

“When the [relationship] really started to get serious . . . I must have been 18 and a half,” the late princess recalls in the special premiering August 22. “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.”

Diana goes on to recount her experience reuniting with Prince Charles in Sussex in 1980, and how it was different from her previous brush with the royal in 1977, when he was dating Diana’s older sister, Lady Sarah.

“I thought, ‘I am quite impressed this time around,’ ” Diana says, before sharing how her future husband—13 years her senior—came on quite strongly that evening, “like a bad rash . . . following me around like a puppy.”

The first clip from the documentary, which was shared exclusively with Vanity Fair, includes archival footage of a teenage Diana being bombarded by press who badger the blushing future princess on the street with questions about a possible engagement.

The excerpt also reveals Diana and her friend James Colthurst reflecting on her unusual courtship with Charles, as well as her pre-princess days living in a flat on Old Brompton Road.

“I was so happy there,” Diana says. “I had three girls living with me. I had the best time of my life.”

Diana - Her Story includes additional footage of Princess Diana speaking candidly about her days before, during, and after her troubled marriage to Prince Charles, as well as interviews with Diana’s closest friends.

To read about the other Princess Diana specials this month—celebrating the late royal on the 20th anniversary of her death—click here.