Rihanna may have postponed her planned May 28 comeback concert in Dubai, United Arab Emirates, but last night she gave a surprise taste of what might have been by dueting with Kanye West at the Metropolitan Museum of Art Costume Institute Gala in NYC, an attendee tells Life & Style.

"It was pure craziness. Bono went onstage to introduce Kanye, who came on and sang two songs. Then, from the background we could hear Rihanna's voice. Everyone was freaking out; no one could believe that she would really perform!"

But Rihanna, who arrived wearing a tuxedo-style Dolce & Gabbana suit, didn't disappoint, wowing the crowd of A-list celebrities and local dignitaries such as New York City Council Speaker Christine Quinn and her partner, Kim Catullo.

"Rihanna joined Kanye for two songs, 'Live Your Life' and 'Umbrella.' She killed it. Everyone was just in awe of how good she looked and sounded. She's back and better than ever!"

Photo Credit: Startraks