“Eternity rings usually celebrate wedding anniversaries or other special occasions. They are a profound promise of life-long companionship.”

Prince William gifting the ring to his wife may have further shown his commitment to the Duchess.

The subtle band is also thought to be worth as much as £2,000.

Tobias added: “From the pictures, this seems to be either a platinum or white gold eternity ring, with a continuing line of round brilliant diamonds thread and grain set into the band, to enhance the brilliance of the stones.