News of the nuptials had been kept top secret, but it seems the jig is up after many of her celebrity friends were spotted arriving in the Italian city on Friday.
One major clue came from Dutch fashion model Marpessa Hennink, who posted a selfie with Kitty with the words: "Team Bride. It's happening finally."
WATCH: Lady Kitty Spencer's exquisite style evolution
It was only in May 2019 that Kitty and Michael went public with their relationship during an outing in New York, despite being linked the previous summer. That August, Kitty was seen kissing Michael after leaving Club 55 in St Tropez.
But who Kitty's soon-to-be husband Michael Lewis? Keep reading to find out…
Who is Lady Kitty Spencer's partner Michael Lewis?
Michael is a South Africa-born fashion tycoon said to be worth £80million. He owns a £19 million mansion in central London, as well as his home in South Africa’s capital.
The 62-year-old comes from a wealthy family thanks to his grandfather founding a furniture retailer in the 1930s, which Michael's father, Stanley Lewis, leveraged to buy a stake in clothing retailer Foschini Group in the 1980s. Michael later took a place on the Foschini Group board and has been chairing it since 2015.
Kitty's model friend Marpessa Hennink hinted at an imminent wedding
Does Michael Lewis have children?
Michael has three adult children, who Kitty will become stepmother too, from his marriage to ex-wife Leola, whom he wed in 1985.
Do Lady Kitty and Michael Lewis have children?
The couple do not share any children, but Kitty has been open about her desire to one day have a family of her own. "I can see myself having children at some point," she told the Daily Mail in 2019. "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."
When did Lady Kitty Spencer and Michael Lewis meet?
It is not clear how Lady Kitty and Michael met, but they are reported to have started dating in 2018, although their relationship was only confirmed when the pair were spotted leaving a New York hotel together in 2019.
Kitty will marry in Rome, Italy
What has Lady Kitty Spencer said about Michael Lewis?
Kitty has remained tight-lipped about her relationship but has spoken about the importance of love in the past.
She previously told Town & Country magazine: "It's not that I don't place an importance on love. It's because, for me, love is the most important thing in the world, and I will protect it with all my heart by not making it a topic of discussion.
"You open yourself up to other people having opinions, and it just isn't relevant to anybody's life but mine and my family's."
Kitty added: "I just look forward to a really happy home life: a happy marriage and happy children. And I feel very at peace that things play out the way they should."
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