That's because the only costume Rihanna needs is a tiara!
The Diamonds singer literally accessorized with diamonds as she walked the red carpet at the 2012 Halloween Carnaval held at the Greystone Manor Supperclub Wednesday night.
She was named the Queen of the Carnaval and she definitely showed off that royal smile of hers!
She's still one of the prettiest princesses we've ever seen! See for yourself and look at more pics of her (below)!
[Image via Starbux/WENN.