The professional tennis player donned a pale pink mid-length dress as she attended the wedding ceremony at Windsor Castle to see her good friend Meghan Markle marry Prince Harry.
Following the royal couple’s nuptials, the star later revealed she had changed outfit for the evening reception.
Having ditched the nude gown, Serena shared a series of photos of herself sporting a jaw-dropping floral ball gown.
And today, the 36-year-old let fans in on a very surprising secret about the glamorous get-up.
Sharing a photo of herself walking outside towards a coach, the star lifted up the floor-length gown.
Unveiling her shoes, Serena revealed that she was actually wearing trainers beneath the magnificent dress.
She captioned the photo: “Little known fact: I often wear sneakers under my evening gown.
“These @maisonvalentino @pppiccioli gave to me last min. I told him be careful I tend to be comfy for long nights.”
It is currently unknown as to whether Serena later changed her footwear before arriving at the second Royal Wedding reception.
The Valentino gown featured a black sleeveless bodice, which billowed into a bright floral skirt.
She teamed the ensemble with a statement gold Bvlgari necklace, which featured a bejewelled green pendant.
Serena opted for the same hair style as earlier in the day, letting her long locks fall in a number of braids.
In a clip shared on her Instagram story, the mother-of-one asked her husband Alexis Ohanian to share his thoughts about her look.
She quizzed: “So what’s the verdict on the braids?”