The model and philanthropist, 30, is the eldest daughter of Charles Spencer, the 9th Earl Spencer, and Princess Diana’s brother. She and Lewis, 62, had reportedly been dating for two years, before their engagement was announced in January 2020.
The ceremony, held at Villa Aldobrandini in Frascati, was attended by the couple’s close friends and family, including Lady Kitty's sisters, twins Eliza and Amelia, and Viscountess Emma Weymouth and her husband Ceawlin Thynn, the Marquess of Bath.
Lady Kitty's brothers Louis Spencer, Viscount Althorp and Samuel Aitken walked her down the aisle, according to the Daily Mail.
Celebrity friends in attendance included singer Pixie Lott, Idris Elba's wife Sabrina Dhowre Elba, and Made In Chelsea star Mark Francis Vandelli, People reports. Elon Musk’s mother, Maye Musk, was also spotted at the wedding.
For her big day, Lady Kitty wore five Alta Moda dresses specially designed by the Italian duo Dolce & Gabbana, for whom she is the brand ambassador.
The brand posted a behind-the-scenes video on their social media.
"@kitty.spencer chose to wear Dolce&Gabbana on the most important day of her life. For this unique event, #DolceGabbana created a number of exclusive handmade gowns, each celebrating the beauty of the bride, the passion for #AltaModa and the absolute joy of the occasion," it said.
The wedding gown, a Victorian-inspired piece, featured a high neck, puff sleeves and a cinched waist, which the bride paired with a lengthy train and hoop earrings.
She later changed into a baby blue tulle gown for the reception, complete with a cape embroidered with cross-stitched flowers.
Among the five dresses was also a double organza hand-painted silk gown embellished with flowers and crystals.
"Once she had received the proposal, she told us she had thought of us immediately, and we were very happy of that," designer Domenico Dolce told Tatler.
"One of the inspirations is definitely her love for Italy. Kitty is in love with our beautiful country and its rich history, art and culture. But she is also a girl who is very attached to her origins, to England; to her heritage of the great Victorian era. And like all the English people, she has a great passion for all kinds of flowers."
Stefano Gabbana added: "Lady Kitty Spencer is a girl who is very respectful of her origins, so she certainly started from her Englishness, her memories, her childhood and the traditions of her country. Then, she also let herself be carried away by her passions and her refined and elegant taste. We accompanied her on this journey full of emotions and it was a real honour for us."
Lady Kitty has a special relationship with Italy, having studied Italian and art in Florence for three years. She first walked for Dolce & Gabbana at their show in Milan in 2017 and has also worked with other brands including Bulgari and Alberta Ferretti.
According to the Daily Mail, guests were treated to a feast and dancing followed by a fireworks display after the ceremony.
While the couple have been linked for a couple of years, Lady Kitty has been guarded about her relationship with Lewis, the fashion tycoon and chairman of South Africa’s Foschini Group.
“I feel less vulnerable when I don’t discuss things like my love life. I just think, ‘Really, what’s that got to do with anyone else?’,” she told Town & Country in May. “It shouldn’t make a difference to anyone’s day. Who I love or don’t love, or have a crush on or don’t have a crush on, or go on a date with, I don’t know why that should be what somebody reads over their cornflakes."