Princess Beatrice's massive ring-and-bow-shaped hat turned heads at the wedding of her cousin Prince William last month.
The Philip Treacy creation has been compared to a toilet seat or a pretzel. Images of the headpiece have been repeatedly digitally manipulated and posted online, featuring - for example - a cat crawling through it.
Funds from the hat's sale will go to UNICEF and Children in Crisis, according to eBay. Beatrice said she hoped whoever bought the hat would have "as much fun with it as I have."
The auction ends May 22.
