Katy Perry Taking Girls' Allison Williams to 2013 Grammys—Not John Mayer!

"She's the hottest date. She's a friend of mine and she's nominated as she should be," the HBO star told Anderson Cooper

This Sunday is officially going to be a Girls night for Katy Perry.

The Grammy-nominated singer has decided to leave her man John Mayer at home and instead take her gal-pal and HBO star Allison Williams to the 2013 Grammy Awards this weekend (hopefully her grandma doesn't get too jealous).

"I am going to the Grammys and Katy Perry is my date," Williams told Anderson Cooper during his Anderson Live today. "She's the hottest date. She's a friend of mine and she's nominated as she should be. I can't wait to go. Obviously she's awesome. She's the best."

These new BFFs met just a few months ago through their boyfriends—Williams has been dating College Humor founder Ricky Van Veen since the spring of 2011—and have been spotted out together on double dates.

So what will Mayer do without his main lady? Maybe some more observing of his past ways?

The crooner told CBS Sunday Morning's Anthony Mason in an interview (airing this Sunday), "I was just a jerk," in regards to his past relationships. "It's very liberating when you finally realize it's impossible to make everyone like you," Mayer said, adding, "I wanted everybody to like me. I thought I was one shuck and jive away in every direction."

Look at John Mayer growing up right in front of our eyes.