Proceeds from the sale of the hat, designed by Irish milliner Philip Treacy, will be split between two charities: the United Nations Children’s Fund, UNICEF, and British charity Children in Crisis.
The princess, the oldest daughter of Prince Andrew and a granddaughter of Queen Elizabeth II, provided one of the most memorable moments of a dramatic day when she stepped out in the eccentric headwear, likened to a giant pretzel.
Other royal-watchers compared the creation to a toilet seat and it has inspired its own Facebook page, “Princess Beatrice’s ridiculous royal wedding hat”, which has a following of more than 143,000 people.
“I’ve been amazed by the amount of attention the hat has attracted,” the princess said in a statement on the auction site.
“It’s a wonderful opportunity to raise as much money as possible for two fantastic charities,” she added.
Treacy, who is now based in London, designed many of the hats on show at the April 29 marriage between Prince William and Kate Middleton, which was watched by an estimated global audience of two billion.
The celebrated designer said he was “delighted, flattered and touched” by the 22-year old princess’s decision to donate the hat to charity.
“I hope that people all over the world will be generous and that this hat will benefit many. A hat is a symbol of positivity,” he added.
The piece is described on the site as “a unique sculptural celebratory headpiece” made of tea rose silk, adding: “This is a gravity defying hat!”
“I hope whoever wins the auction has as much fun with the hat as I have,” the young royal said.