The model, 30, shares a close bond with her royal cousins, Prince William and Prince Harry, but despite Italian journalist Fabio Polli revealing that the Duke and Duchess of Cambridge were expected to arrive in the city on Saturday morning, it seems neither royal brother was in attendance.
WATCH: Lady Kitty Spencer's style file
The wedding was still attended by a number of Lady Kitty's high-profile friends like Viscountess Emma Weymouth, Sabrina Elba and Pixie Lott.
Lady Kitty Spencer and her sisters at William and Kate's royal wedding
It's thought Lady Kitty had to delay her nuptials to Michael due to the pandemic, after they got engaged in 2019.
And she isn't the only family member who has had to delay her big day. Kate's younger brother, James Middleton, previously revealed that he had to postpone his wedding to fiancée Alizee Thevenet twice last year.
Lady Kitty was among the guests at Prince William and Kate's wedding in April 2011, attending the ceremony at Westminster Abbey with her father, Charles Spencer and his third wife, Karen Gordon, and Lady Kitty's siblings, twins Lady Amelia and Lady Eliza, and Louis, Viscount Althorp.
She also topped the best-dressed lists in a stunning hand-painted green Dolce & Gabbana dress at Prince Harry and Meghan Markle's royal wedding in May 2018.
Make sure you never miss a ROYAL story! Sign up to our newsletter to get all of our celebrity, royal and lifestyle news delivered directly to your inbox.