He took to Instagram with the photo, showing the couple holding hands on a walk, and revealed a close-up of the impressive gem.
WATCH: Brooklyn Beckham gets engaged
Experts had previously valued the diamond at approximately £120,000 - £160,000, after surmising that it could be a 4.5-5 carat diamond in a classic solitaire setting.
Nicola Peltz's engagement ring
Nonetheless, gemologist Alexandra Michell from Prestige Pawnbrokers told the Mail Online: "The central stone is approximately 5cts and appears colourless, and with a classic emerald cut, it is usually a good indication that the diamond is very clean with minimal imperfections.
"The emerald cut solitaire style is a timeless classic and has been worn by many celebs over the years from Grace Kelly and Elizabeth Taylor to Jennifer Lopez, Angelina Jolie and Beyonce.
"I believe the retail price for this engagement ring could be in excess of £350,000."
Brooklyn gave a first look at the ring last year
Brooklyn previously offered fans a glimpse of the diamond when he posted a phot of his pet dog, and Nicola's hand in the background.
It would make sense that Brooklyn's mother Victoria inspired the ring Brooklyn chose for Nicola, as David first proposed to his wife with a very similar three-carat marquise-cut diamond on a yellow gold band.
Victoria Beckham owns a similar engagement ring
Over the years, Victoria went on to invest in various styles, while David gave her most as gifts. Now, she owns an incredible 14 engagement rings.
Brooklyn and Nicola got engaged in July 2020, and Victoria shared the news on Instagram with a photo of the couple at the Beckhams' country home.
She captioned it: "The MOST exciting news! We could not be happier that @brooklynbeckham and @nicolaannepeltz are getting married! Wishing you so much love and a lifetime of happiness. We all love you both so much x @Davidbeckham @romeobeckham @cruzbeckham."
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