Butt Day!' Kate Upton Bares Her Entire Backside in Sheer Dress

The 23-year-old supermodel shared a booty-baring photo, posing in a see-through, flowing burgundy dress. "Happy Sunday! #buttday #bruceweber #sundayfunday," she wrote.

Model Kate Upton bares her naked butt in sheer dress

The cheeky pic isn't the first of its kind this summer. In fact, so many celebrities are baring their bums on Instagram, it's starting to become a trend.

Justin Bieber flashed his butt earlier this month, only to take it down after deciding that it might offend his younger fans.

Chrissy Teigen also showed off her supermodel butt in a thong bikini.

Chrissy Teigen shows off her famous butt

Vodafone: Enjoy unbeatable values on 4G Devices and the fastest internet