It's the Oscars of Fashion -- and Rihanna forgot to wear underwear!

Monday night in NYC, The Council of Fashion Designers of America is honoring the people behind some of the best red carpet looks, as awards are handed out for excellence in womenswear, menswear and accessories.

And while designers will be taking home the bulk of the statues tonight, there were some killer celeb sightings at the annual event.

Rihanna, who will receive the Fashion Icon Award, showed up in a stunning (and completely see-through!) gown that showed off her nipples and chest tattoos. She kept her other lady bits covered with a nude thong and a pink fur.

Wait until you see it from the back! Check out the INSANE rear view in the gallery above.

After she collected her award, RiRi showed off her moves in the revealing ensemble on Instagram -- twerking in the see-through dress.

PHOTOS: See Rihanna's Most Revealing TwitPics

Other sightings included Solange Knowles, in her first public appearance since her now-infamous blowout with Jay Z, Blake Lively, The Olsen TwinsLupita Nyong'o, Alessanda Ambrosio, Keri Russell, Olivia Wilde and Busy Phillips.

But the most surprising celeb on the carpet was Mango! Chris Kattan stepped back into his famous "Saturday Night Live" character's shoes for the evening -- and we're loving it.

We'll keep updating the gallery above as more photos come in. Tell us who you think is best dressed in the comments below!

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