Pixie Lott, the Marchioness of Bath and Sabrina Dhowre Elba were reportedly among the attendees.
The 30-year-old model has been dating Lewis, 62, for more than two years but they’ve largely kept their relationship out of the spotlight.
Photographs show Lady Kitty wearing a Victorian-inspired white lace wedding dress on her special day.
She walked down the aisle with her brothers Louis Spencer, Viscount Althorp, and Samuel Aitken
Her elegant gown featured a high neck, puff sleeves, bridal buttons, a cinch waist and a decadent long train.
Mr Lewis owns the high street fashion chains Whistles and Phase Eight.
News of the couple’s relationship broke in 2018 with Mr Lewis proposing in December 2019.
Lady Kitty posted a picture on Friday that appeared to show her hen night.
The image shows a group of women in colourful wigs as they strutted the streets in long gowns with their backs away from the camera.
Her caption read: “Money Heist.”
Lady Kitty’s wedding gown was made by fashion house Dolce and Gabbana, the Mail on Sunday reports.
She was appointed the brand’s global ambassador earlier this year.
Watch: British Royal weddings through the years