While Diana simply replied: "Of course," the Prince of Wales joked: "Whatever 'in love' means." The moment was recreated for the popular Netflix series, and saw Diana worrying about the comment over the phone to her friends during a later scene.
WATCH: Prince Charles' 'whatever in love means' comment during engagement interview
Althought the show almost certainly fictionalised the future Princess of Wales' reaction, the comment did absolutely take place in real life. Watch the video above to see the real-life moment.
Fans have been full of praise for the new series, which introduces Emma Corrin as Diana. Tweeting about her portrayal as the Princess, one person wrote: "Emma Corrin is the perfect Diana. She captures her shy naivety and her kindness with an air of entrenched sadness. My one concern watching is that she has way too much chemistry with Josh O’Connor."
The moment was recreated in The Crown season four
Josh, who plays Prince Charles on the show, opened up about the show's similarities to real life, telling Sky News: "I wouldn't have been massively interested in doing it I don't think, if we were doing some sort of mimicry or keeping too much to the real people, because The Crown isn't that.
"I mean, what's interesting about The Crown is the stuff we don't know, and it's the fiction, it's the speculation of what happened behind the closed doors."
Emma also chatted about whether she thinks Princes William and Harry will be tuning in. She explained: "I try not to think about whether people watch it because I think that's a slippery slope. You can't really control if they do and also if you start thinking about, 'I wonder what they'll think'... It's kind of, yeah, it's quite stressful."