"I've been amazed by the amount of attention the hat has attracted," Beatrice is quoted as saying in the auction listing. "It's a wonderful opportunity to raise as much money as possible for two fantastic charities. I hope whoever wins the auction has as much fun with the hat as I have."
Although some on the hat's Facebook page had predicted a last-minute bidding frenzy, the winning bid of 81,100.01 pounds (about $131,341) was placed hours before the end of the auction.
Beatrice, the daughter of Prince Andrew and Sarah Ferguson, the Duchess of York, wore the hat to the April 29 wedding of Prince William and Catherine Middleton. It was designed by milliner Phillip Treacy.
"A truly individual, fun but elegant wedding bow becomes the fascinator form," says the description in the auction listing. "This statement piece is worn on the front hairline secured by a clear wire headband that is easily disguised by the wearer's hair. This is a gravity-defying hat."
The listing also shows some of the tongue-in-cheek photos created and posted online, such as one with a cat crawling through the front of the hat. It also inspired a tribute song.
Proceeds from the auction benefit The Little Bee Initiative, a campaign set up by the princess to benefit UNICEF UK and Children in Crisis, according to the listing.
"I've been surprised by the overwhelming response to 'the hat,' " Treacy said in the auction listing. "... I'm delighted, flattered and touched by HRH Princess Beatrice'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."
The auction was managed by Auction For A Cause, an auction management service that specializes in "high-profile promotional auctions for charities, nonprofit organisations and brands," according to the listing's frequently asked questions.
Bidders were required to be preapproved, according to the listing, and at least 18 years old.
Reaction to the auction on the hat's Facebook page was positive.
"Gracefully done, Princess B," one poster wrote, "auctioning off the monstrosity for a good cause with dignity and humor."
"Absolutely fabulous!" another person wrote. "How cool is she for doing this?"