Kitty Spencer was spotted wearing a diamond ring now estimated to be worth up to £300,000 on her wedding finger, as she was spotted with her 60-year-old fashion tycoon beau in Cape Town yesterday.

Princess Diana's niece, who only turned 29 last month, has been dating fashion tycoon Michael Lewis, who is six years older than her father, Earl Spencer, 55, since last spring.

The couple went public with their relationship during a stroll through New York City in May and were seen kissing after leaving Club 55 in St Tropez in August.

And now an expert has revealed that the society model, who is 32 years younger than South Africa-born multi-millionaire, Michael Lewis, who turns 61 this month, was wearing an emerald cut diamond ring with an estimated '30 carats of flawless' diamonds.

Kitty Spencer was spotted wearing a diamond ring now estimated to be worth up to £300,000 on her wedding finger, as she was spotted with her 60-year-old fashion tycoon beau in Cape Town yesterday

Speaking to MailOnline, appraiser Oliver Horner from Prestige Pawnbrokers of Channel 4’s Posh Paw, said: 'This gorgeous full hoop diamond full band engagement ring is of extremely high quality.

'The full band is set with large emerald cut diamonds, each stone looks to be approximately one and a half carats and I would estimate the total diamond weight of the ring to be between 25 and 30 carats.

'Judging from the image the diamonds look to be of exceptional quality and I estimate a clarity grade to be between flawless and VVS1 and to be of D to F colour which is the very best.

'I believe a ring of this exceptional quality would have an would cost between £200,000 - £300,000 maybe even more given the provenance of such a piece.'

An expert has revealed that the society model, who is 32 years younger than South Africa -born multi-millionaire, Michael Lewis, who turns 61 this month, appeared to be wearing an emerald cut diamond ring with an estimated 30 carats of emerald cut diamonds

Although she was previously spotted with the ring on last November, this is the first time she has worn it on her left-hand wedding finger.

The appearance comes just a few weeks after insiders told the Daily Mail that Kitty agreed to marry the father-of-three, after he reportedly proposed to her before Christmas.

Kitty grew up in Cape Town, and spent Christmas, her birthday and New Year's Eve in South Africa, where Michael is also based.

Michael has three adult children and was previously married to a woman named Leola in 1985.

Kitty, who was spotted at the tycoon’s £19 million mansion in central London last summer, told the Mail at the time that she didn’t feel ‘in any rush’ to start a family.

‘I can see myself having children at some point,’ she told me, ‘but I’m only in my 20s. I do have friends my age who are having children, and they are so, so, sweet, but I think everyone should do things in their own time.’

Lewis' previous wife, Leola, signed a prenuptial agreement but it's not yet known whether Lady Kitty will do the same.

Lady Kitty Spencer has shared a glimpse at her sun-soaked vacation in South Africa, after seeing in her birthday and the festive period abroad. Princess Diana's niece, who turned 29 last month, took to Instagram this week to post a picture of her glamorous surroundings in Western Cape

Lady Kitty's last boyfriend was Italian property magnate Niccolo Barattieri di San Pietro, who was also significantly older than the socialite.

At the beginning of the month one of her friends told the Daily Mail: '‘Michael proposed to Kitty before Christmas.

‘She’s been in Cape Town for the holidays and told her mother and the rest of the family. Michael is loved by all of them. Despite his wealth, he’s very humble and low key.’

It's not yet known whether Lady Kitty will convert to Judaism, Mr Lewis' faith, before the big day.