Prince Harry gave Diana's engagement ring to William, to propose to Kate

Princess Diana's sapphire and diamond engagement ring is a stunning piece of jewellery.

No one was surprised, therefore, when Prince William used his late mother's ring to propose to Kate Middleton, but what many don't know is that the ring actually belonged to Harry.

Kate Middleton, wearing her engagement ring which once belonged to Diana, Princess of Wales, on the day her engagement to Prince William was announced. Photo / Getty Images

A new Amazon Prime documentary, The Diana Story, reveals that Diana's engagement ring was left to Harry when she died in 1997. The documentary goes on to confirm that Harry gave up the ring, allowing William to give it to Kate Middleton when he proposed.

In the revealing doco, Princess Diana's former butler, Paul Burrell, confirms that the ring did technically belong to Prince Harry, but he wanted Kate to have it.

Burrell states in the documentary: "Harry said to him: 'Wouldn't it be fitting if she had Mummy's ring?'"

Princess Diana is pictured here in 1991 wearing the sapphire and diamond engagement ring that Charles gave her. Photo / Getty Images

He added: "Then one day that ring will be sat on the throne of England. Harry gave up his precious treasure.

"His one thing he kept from his mother, he gave to his brother. That's selfless, kind and exactly who Diana was."

When Harry later met Meghan and decided to propose he no longer had the precious ring, but he was able to honour his mother in a different way.

The ring Harry gave to Meghan is one he designed himself. It has a large central diamond, sourced from Botswana where the pair had travelled together, and, more significantly it features two diamonds from Diana's collection.

Harry may have given up his mother's engagement ring to Kate, but he included two stones that belonged to Diana in the ring he had made for Meghan Markle. Photo / Getty Images

At the time of the engagement announcement Meghan said that the ring ensured Diana was "with us on this crazy journey together".

She said: "Everything about Harry's thoughtfulness and the inclusion of Princess Diana's stones and obviously not being able to meet his mum, it's so important to me to know that she's a part of this with us."