Princess Beatrice of York
Beatrice's appearance at Kate Middleton and Prince Williams 2011 nuptials had the whole world talking. Her now infamous Philip Treacy hat garnered so much media attention, the princess later sold it on eBay and raised $130,000 for charity.
Princess Eugenie of York
As for Beatrice's younger sister, Eugenie, she too went all out for Kate and Wills big day. Although not as famous as Beatrice's, many fans couldn't help but comment on the feather detailing.
The daughter of Princess Anne and Captain Mark Phillips attended her cousin William's wedding in a Phillip Treacy outfit and slanted fascinator. Although stunning, Phillips gained attention in this outfit after her inability to move her hand from her head once outside.
Queen Margrethe II of Denmark
Sporting an entirely blue ensemble for Wills and Kate's wedding - one of the day's most prominent colour choices - wore a blue hat with swirling feathers.
Camilla, the Duchess of Cornwall
Camilla Parker-Bowles, the wife of Prince Charles, wore an outfit by Anna Valentine on her wedding in 2005 at The Guildhall at Windsor Castle in Berkshire, England. To complement the outfit, she wore a spray of golden feathers created by Philip Treacy, instead of a traditional tiara.
The daughter of Duchess Camilla wrote a gold fascinator for the civil ceremony of Prince Charles and her mother.
Soap opera actress Katherine Kelly attend Zara Phillips and Mike Tindall's wedding in 2011 sporting an orange and pink H'atelier hat that stood out amongst the crowd.
TV presenter Kirsty Gallacher opted to dress in an usual jade fascinator for Zara's wedding, pairing it with nude heels and a multi-coloured dress.
Another bold hat choice for the Princess of York. The multi-colored butterfly fascinator by Philip Treacy matched her rainbow-hued dress at the wedding of Peter Phillips.
Princess Katharina Nina von Hohenzollern
For the wedding of Georg Friedrich Ferdinand Prince of Prussia to Princess Sophie of Prussia in 2011, Princess Katharina opted for a whimsical fascinator.
Duchess of Lugo
Infanta Elena of Spain attended the wedding of Princess Alexia of Greece and Carlos Morales Quintana at the St. Sophia Cathedral in London in 1999 in a wide-brimmed hat covered in feathers.
While attending William and Kate's wedding, Victoria Beckham chose to wear a navy fascinator that sat directly on top of her forehead. The navy hat with navy embellishments matched her billowing dress.
Why do guests wear hats to a royal wedding?
Royal protocol dictates that women must wear hats to all official occasions. According to the BBC, the rule dates back to before the 1950s, when women rarely showed their hair in public.
Prince Harry and Meghan Markle's upcoming wedding on May 19 will certainly be full of memorable looks from head to toe.