Prince Charles had only met Lady Diana Spencer 12 times when he proposed.
She was just 20 years old, more than a decade younger than her future husband, when she was invited to Windsor Castle for a visit that would change her life forever.
When she left, she was engaged to the future king and had officially begun her royal journey.
As she arrived at the historical royal home, Charles told her he had "missed her so much", before the couple made their way to the nursery.
Speaking in a Channel 5 documentary Charles and Di: The Truth Behind Their Wedding, royal expert Ingrid Seward explains that the big proposal was far from romantic.
She claims that Diana actually started laughing when he asked the question.
She said: "She burst out laughing, I think that was probably her nerves.
"She didn't think it was the most romantic of proposals but she had the proposal."
Royal biographer Christopher Wilson added: "She was completely bowled over by this, didn't see it coming."
In a later interview Diana revealed further details about the proposal.
She said: "He said do you realise that one day you'll be Queen. And I said 'I love you so much, I love you so much'.
"He said 'whatever love means'. He said it then. So I thought, that was great. I thought he meant it."
And the moments after Diana said yes weren't exactly romantic either, and rather than celebrating Charles picked up the phone.
Mr Wilson said: "He didn't pick her up in his arms and embrace or do any of the things we might do when we propose marriage to the one that we love.
"He rang his mum, simply to say there, I've done it now. You've asked me to get married to somebody and I've fixed it.
"What he'd done was he'd finally found a wife."
After popping the question, Prince Charles presented Lady Diana with a selection of rings by Garrard of Mayfair, the Crown Jeweller at the time.
She picked the white gold ring with 14 solitaire diamonds surrounding the famous sapphire.
But there was a problem with it - it wasn't bespoke.
The ring had actually featured in a catalogue which means, unlike most royal engagement rings, it wasn't unique, reports the Sun.
In fact, anyone could have bought exactly the same ring - which didn't go down well with the royals or their staff.