Katy Perry, Allison Williams Grammys 2013 Double Date -- All the Details

USMagazine, Monday, February 11, 2013, 2:00pm (PST)

Katy Perry may have walked the Grammys 2013 red carpet with her good friend Allison Williams -- but it wasn't just a ladies' night! Perry joined boyfriend John Mayer, and Williams met up with boyfriend Ricky Van Veen inside the show Sunday, Feb. 10.

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During a Feb. 7 appearance on Anderson Cooper Live, Williams, star of HBO Girls and daughter of NBC Nightly News anchor Brian Williams, revealed she was going to be Perry's date to the Grammys. "She's the hottest date," Williams, 24, said. "She's a friend of mine and she's nominated as she should be. I can't wait to go."

The two pals held each other tight and looked gorgeous while posing for pictures together at L.A.'s Staples Center. Perry, 28, wore a cleavage-baring Gucci gown, while Williams styled a more modest Kaufman Franco dress. Once inside the show, the ladies joined their real dates and continued the fun from the first row. The couples are no strangers to double dating together. In mid-December the Girls actress and her College Humor founder beau joined Perry and Mayer, 35, for dinner at The Lion in New York City.

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During the Black Keys' performance of "Lonely Boy," the four pals (plus Ellen DeGeneres and wife Portia de Rossi, who were also sitting in their row) were the only stars to stand up to enjoy the song, an eyewitness tells Us Weekly. Williams also brought Perry over to meet her Girls costar Lena Dunham, who was attending the award show with boyfriend Jack Antonoff, the guitarist of Fun. "They all gave each other huge hugs," the insider says.

While presenting the award for Best New Artist onstage, Perry joked, "I was not even nominated in this category and I have my own eyelash line. Take that, Bon Iver," she said of the beloved indie rocker who won the award in 2012. After the joke, Perry retweeted a fan's comment: "I bet you $10 John Mayer and Ricky Van Veen wrote that 'Take that, Bon Iver' joke."

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Once the show ended, the double date continued at the Warner Music Group After Party at Chateau Marmont in Hollywood. Perry and Williams were joined at their table by Selena Gomez and her friend, actress Samantha Droke, for a little girl talk, but were interrupted by Perry's boyfriend.

"John came over and kissed Katy on the lips," the eyewitness tells Us. "These two are really into each other and they're super cute together."

This article originally appeared on Usmagazine.com: Katy Perry, Allison Williams Grammys 2013 Double Date -- All the Details