Eugenie's ring is a rare sapphire and a nod to the Duchess of York

Princess Eugenie's engagement ring contains the rarest of all sapphires - and is perhaps a tribute to her mother.

Eugenie, who is to wed long-term boyfriend Jack Brooksbank, showed off the ring at Buckingham Palace in official photographs marking their forthcoming wedding.

Her ring - an oval padparadscha sapphire surrounded by diamonds, set on a gold band - is strikingly similar in shape and design to Sarah, Duchess of York's engagement ring.

But while the duchess's central stone was a red ruby, Eugenie's is a pink sapphire.

Recognisable by its pinkish-orange colour, the padparadscha is the rarest of all sapphires and usually comes from Sri Lanka.

According to the Natural Sapphire Company: "Nothing brings to mind blooming flowers like padparadscha sapphires.

"Named after the colour of a Lotus blossom, the pinkish orange glow of these stones are hypnotising."

Eugenie is close to her mother. The duchess split from the Duke of York in 1992 and they divorced in 1996, but remained good friends, prompting speculation they might one day remarry.

In 1986, Andrew gave Sarah Ferguson, as she was then known, the ring when he proposed, and chose the Burmese ruby to match her red hair.