: Diana chooses the blue sapphire ring, which was actually a stock item for sale from the jeweler Garrard's rather than a unique royal heirloom.
Key details about this "proper piece" in the episode include: [S4E3] Fairytale
: For the show, a high-quality reproduction of this ring was created, which was later sold at a specialized The Crown Auction . "Fairytale" EXPLAINED - The Crown S4E3 Recap : Diana chooses the blue sapphire ring, which
: The Royal Family's reaction suggests her choice was slightly unconventional because it was not a one-of-a-kind antique. [S4E3] Fairytale
In The Crown Season 4, Episode 3, titled "," the "proper piece" refers to the iconic engagement ring Lady Diana Spencer selects from a tray of options presented by the royal jeweler.