Instead of choosing a traditional diamond, Eugenie was given a jewel with a central red sapphire.
The ring could be worth a huge sum of money, according to Lorna Haddon, head of diamonds and jewellery at Beaverbrooks.
“Eugenie’s engagement ring features a classic gold band set with a stunning padparadscha sapphire,” she stated.
“The rare gem is nestled within 10 brilliant cut diamonds and two pear cut diamonds to emphasise the central gem and create an eye-catching finish.
“The slim gold band accentuates the central piece and draws the eye straight to the gorgeous and unusual sapphire.
“Eugenie’s historic ring is estimated to be worth around the £100,000 mark, due to its rare padparadscha sapphire.”
The expert commented on the “unusual” but eye-catching style of the ring.
It was believed to be partly designed by Jack himself and it seems he may have used another royal ring for inspiration.
At the time, it was thought to cost around £25,000 but is likely worth more now due to its royal significance.
Sarah and Prince Andrew officially divorced in 1996.
They had two children together, Princess Eugenie and Princess Beatrice.
Both royal women are now married and have impressive engagement rings.