Sarah Ferguson arrives for the wedding. (Toby Melville/Pool via AP)

Princess Eugenie and Casamigos ambassador Jack Brooksbank tied the knot during a moving ceremony at St George’s Chapel in Windsor Castle.

While the royal fans eagerly waited to see the bride's wedding dress, all eyes were on what the guests were wearing on arrival.

The guest list included A-listers such as Naomi Campbell, Cara Delevingne, Demi Moore and Robbie Williams.

Meghan, the Duchess of Sussex, disappointed in a rather drab outfit. Unlike her sister-in-law, Kate Duchess of Cambridge, who wore a more cheery fuschia colour dress.

Kate, Duchess of Cambridge, Britain's Prince Harry and Meghan, Duchess of Sussex, from left, attend the wedding of Princess Eugenie of York and Jack Brooksbank in St George’s Chapel, Windsor Castle, near London, England, Friday Oct. 12, 2018. Picture: AP

Models Cara Delevingne and Naomi Campbell both wore striking outfits but for very different reasons. Cara broke tradition by boldly wearing a suit and top hat. While Naomi wore an exceptionally tall and the fanciest grey hat at the wedding.

Cara Delevingne. Picture: AP
Supermodel Naomi Campbell. Picture: AP

Actress Demi Moore opted for a chic crimson ensemble.

Demi Moore arrives ahead of the wedding of Princess Eugenie of York and Jack Brooksbank at St George’s Chapel. Picture: AP

Mother of the bride, Sarah Ferguson, stepped out in a bright green ensemble with a green and gold hat that's already had quite a response on social media. These are a few reactions to the meme-worthy hat.