The couple, who had been dating for the past seven months in what was their second chance at love, have again parted ways, a source confirms to PEOPLE.
The split comes less than a month after Perry, 28, was spotted wearing a ruby from Mayer, 35.
They were first linked last summer, less than a year after Perry and Russell Brand divorced. And while Mayer and Perry split briefly last August, they quickly reconciled and embarked on what seemed to be a growing love affair.
They even spent Christmas together with her family.
As recently as last month, Mayer was upbeat about the relationship, calling it "very human" and even speculating on the idea of marriage.
Pick up PEOPLE magazine this week for more about Katy and John's split