In recent weeks, the two have been spotted out together discreetly hiding their budding romance, but now they're a full-blown couple and don't care who knows.
The pair were photographed last week in Beverly Hills making out poolside, and they were not trying to hide their affection for each other.
"They hugged each other and splashed around," a source told Us Weekly. "They were all over each other, making out! Neither of them is exactly shy."
"Katy says she's officially dating John, not just hooking up," one insider told the magazine. Another source says the 27-year-old "doesn't want to get her heart broken again, but she feels a real connection and wants to see where things go."
After her marriage to comedian Russell Brand ended, the singer had a couple brief flings, but she's now ready for something more, and so is 34-year-old John Mayer. He hasn't been in a serious relationship since 2009 and told Rolling Stone, "I haven't had a girlfriend in a long time.... Now I feel like I'm extremely open to love."
Apparently Katy has always had a thing for John. A source said she had a "major crush" on him in 2009. And, adds a John pal, "John has always thought Katy was really sexy. He loves curvy girls."
What do you think of John and Katy as a couple?