Williams, who stars in the HBO comedy series, confirmed her high-profile date to Anderson Cooper on Thursday's "Anderson Live!"
"I am going to the Grammys and Katy Perry is my date," she said. "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."
Perry hit the red carpet two years ago with then-husband Russell Brand and her adorable grandmother. She flew solo at last year's awards and has been dating Mayer on and off since June.
She's nominated for solo performance for "Wide Awake" this year.
The girls reportedly met through their boyfriends: Williams is dating Ricky Van Veen, the founder of College Humor, and the couples have reportedly double-dated, according to E! News.
As for Mayer, his interview with CBS's "Sunday Morning" will be airing before Sunday's 55th Grammy Awards; watch for him to address his "jerk" status. He's also slated to present at the Grammys, so we wouldn't be all that surprised if he crashed Perry and Williams' girls night out.
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