The couple began dating in summer 2012 but have called it quits, according to Us Weekly.
"It's sad," says a source, adding that they could still reconcile. "It's not over until it's over. You have to see how things play out."
Another source agrees that they could still patch things up, saying: "She's leaving the window open. They have both been so focused on work."
Katy, who is 28, and John, 35, have had some ups and downs during their relationship, as they apparently split up last August before getting back together the following month.
However, the two had been doing quite well lately, and they had even sparked engagement rumors when she was spotted wearing a ring from him on that finger on Valentine's Day.
As far as their previous romances, Katy was married to Russell Brand for just over one year, while a list of John's former ex-girlfriends would go on for about eight pages.
We're wishing these two the best — and we'll be waiting on
the world their relationship status to change... for the better.
Source: Us Weekly