Beyonce Knowles attends the "Schiaparelli And Prada: Impossible Conversations" Costume Institute Gala at the Metropolitan Museum of Art on May 7, 2012 in New York City. Credit: Kevin Mazur/WireImage.com Girls' night at the Boom Boom Room with Beyonce and Solange ! Surrounded by dozens of A-listers -- Gerard Butler, January Jones, Kirsten Dunst and beau Garret Hedlund, Lily Collins, Kristen Stewart, Ian Somerhalder and Nina Dobrev, Emma Roberts and more -- the singer and Blue Ivy's mom, 30, was the biggest star of them all at Prada's "after after party" for Monday's Met Gala, held at the Boom Boom Room at the Standard Hotel in downtown Manhattan. PHOTOS: What all the stars wore at the Met Gala With sister Solange Knowles as her date and other pals, the "Love on Top" singer provoked a big stir with the crowd as she arrived past midnight. With husband Jay-Z sitting this one out, the mother to Blue, 5 months, was in a great mood as her p...