Granted, it's hard for Ms. Clooney merely to blend in, but her jauntily tilted and perfectly matched wide-brim hat, displaying a dainty veil in front, brought gasps both online and in the crowd that lined the wedding route.
The 64-year-old adhered perfectly to the dress code on Prince Harry and Markle's wedding invitations, which asks that female attendees sport a "day dress and a hat", while males are expected to wear a "morning suit or lounge suit".
Following the service, Queen Elizabeth II was to host a lunch in the castle's St. George's Hall for the 600 guests.
Meanwhile, Oprah Winfrey was spotted making her way into the chapel for the star-studded ceremony.
According to Ms King, Winfrey contacted Stella McCartney who "whipped together" a pink alternative. George and Amal Clooney turned up a little while later, as did David and Victoria Beckham, and Kate Middleton's sister Pippa Middleton, with her husband James Matthews.
Amal and George Clooney arrive at St George's Chapel at Windsor Castle for the wedding of Meghan Markle and Prince Harry.
The talk show icon has no clear connection to Markle, Harry, or the royal family.
Alexi Lubomirski Kensington Palace via AP Harry and Meghan were seen with their bridesmaids and page boys
1025: Members of the royal family will begin to arrive and will enter the chapel via the Galilee Porch to be met by the Dean of Windsor.
The Wrinkle in Time star was one of the first celebrity guests to arrive at the Windsor Castle chapel.
Oprah Winfrey arrives at St George's Chapel at Windsor Castle before the wedding of Prince Harry to Meghan Markle, May 19, 2018, in Windsor, England.
Markle will be accompanied by her mother, Doria Ragland, when she is driven to the chapel, and many of her closest friends and some co-stars from "Suits" will be in the audience.
Meghan Markle's friend, actor Patrick J. Adams and wife Troian Bellisario arrive for the wedding ceremony of Britain's Prince Harry, Duke of Sussex and United States actress Meghan Markle at St George's Chapel, Windsor Castle, in Windsor, May 19, 2018.
She was also wearing an Angela Kelly hat, using the same lime silk tweed with sinamay adorned across the crown with handmade lace crystals and pearls made by Lucy Price.
Earl Spencer, brother of Princess Diana, his wife Karen and his daughter Kitty were at the chapel as was Tom Parker Bowles, the son of Prince Charles' wife Camilla from her first marriage.