The Princess of Wales paid a sweet tribute to her husband, Prince William with one subtle move during their latest appearance, according to a jewellery expert.

Princess Kate delighted royal fans on Sunday after she appeared alongside William in a sweet video, joined by other celebrities and former athletes, and praised Team GB at the Olympic Games as the sporting event in Paris came to a close.

The future Queen looked casual and chic in her beloved Breton striped top and sported minimal jewellery.

But it was the ring on her finger which caught everyone's attention.

Kate is usually seen wearing her iconic diamond and sapphire engagement ring but this time she sported a new ring, which according to the experts, may just very well be a hugely sentimental ring between her and the Prince of Wales.

Jewellery specialists at UK retailer Steven Stone said the new ring is most likely the royal's promise ring - which was given to her by the Prince of Wales many years ago and is estimated to be worth around £1,500.

Promise rings usually symbolise love and commitment between a couple.

William gave Kate a promise ring during the early days of their courtship when they were students at St Andrews University in Scotland.

Kate's promise ring is set on a rose gold Victorian band and features two garnets which are the Princess of Wales's birthstone for January, and pearls to represent William's birthstone for June.

Garnets are known to symbolise perseverance and strength and are traditionally known as commitment stones, which reinforces the meaning behind the ring, while pearls have long been associated with purity, humility and innocence.

According to the experts, Kate's promise ring may be more practical than her engagement ring, which features a 12-carat stone and is more susceptible to everyday wear and tear.

Maxwell Stone, of Steven Stone, said: "While Kate's engagement ring is undoubtedly her most iconic piece of jewellery, it wasn’t the first ring she received from Prince William.

"During their university days, William gave Kate a promise ring, and though it’s hard to be certain, recent footage of the royal couple suggests she may be wearing this sentimental piece again.

"Unlike Kate’s 12-carat engagement ring - which she typically removes during physical activities, sports, or any situation where there’s an increased risk of damage or loss - this ring is more practical for daily wear."

The jewellery expert added: "While its sentimental value is priceless, I would estimate the monetary worth of Kate’s promise ring to be around £1,500."