Prince Harry and Duchess Meghan reportedly "became secretly engaged in August 2017".
Although the prince previously said during the couple's engagement interview in November 2017, that he had proposed "earlier this month", it has now been alleged that he and Meghan actually got engaged three months prior to the official announcement.
The claim has been made in new book 'Finding Freedom', written by royal reporters Omid Scobie and Carolyn Durand.
A new extract from the tome, published in The Times and The Sunday Times, also revealed that Harry, 35, was the first to say "I love you", just three months after they first started dating, and Meghan, 38, quickly responded with "I love you, too".
The pair enjoyed their first date at Dean Street Townhouse in Soho and quickly became smitten with each other, with Harry convincing Meghan to join him on a trip to Botswana.
A friend said: "She came back smiling and just completely spellbound," and Meghan reportedly told her pal: "I've never felt that safe, that close to someone in such a short amount of time."
The source added: "By then, they were each already dancing around the idea that this just may be a forever thing."
A spokesman for Harry and Meghan has insisted the couple did not contribute to the book, stating: "The Duke and Duchess of Sussex were not interviewed and did not contribute to Finding Freedom. This book is based on the authors' own experiences as members of the royal press corps and their own independent reporting."
And author Scobie said: "The book doesn't claim to have any interviews with Harry and Meghan. And nor do we.
"There's no on-the-record interviews with the couple. I think that you can tell from the reporting, my time around the couple is enough for me to know my subjects."
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