The Happy hitmaker won four trophies at the music prizegiving last month (Jan14), but it was his oversized accessory that had Tv viewers talking, and now he's giving up the bizarre headwear for charity.
In partnership with auction website eBay.com, Williams is offering up the Vivienne Westwood-designed hat to benefit his From One Hand to Another non-profit organisation.
Williams says, "I'm giving up the Buffalo Hat I wore to the Grammys to help undeserved kids get the educational tools they need. Our organization, From One Hand to Another, is committed to bringing kids experiences that ignite their passions, challenge their minds and prepare them for success."
The hat went on sale on Thursday (20Feb14), and within hours, bids for the item had reached $10,500 (£6,301).
The auction runs until 2 March (14).