According to a new report from E! News in the US, the couple called time on their on-off relationship "within the last few days."
No other details were included in the report.
Los Angeles-based Katy has been travelling over the past week or so, arriving in the UK last week for a performance at the Brit Awards 2014, before jetting over to Italy to walk the runway at Milan Fashion Week.
So far, neither Katy nor John have said anything about the latest split report and whether it's true and, just to muddle things further, it came amid another report in the UK that they were planning a summer wedding in Santa Barbara, California.
Although they never confirmed an engagement, Katy set tongues wagging about a proposal while attending the Elle Style Awards on 18 February wearing a diamond ring on her engagement finger.
Whatever is happening in Katy's personal life, she's all business right now, tweeting overnight about new additions to her 'Prismatic World Tour' in the US and bringing the show to Australia and New Zealand in November.
She also looked in good spirits on Saturday, 22 February when she attended a Miley Cyrus concert in Los Angeles and was snapped giggling after sneaking a kiss from the lady herself mid-performance.
John, meanwhile, is gearing up for tour dates across Australia, New Zealand, Japan, South Korea and Europe, including London, from April through June.
If they have split, it would come as a surprise to fans, as they were seen looking as happy as ever on a Valentine's Date this month, and in December 2013, they were blissfully happy during their first joint TV interview.
Promoting their duet 'Who You Love', which appears on John's latest album, the couple chatted openly about their relationship, including their first date.
The couple began dating in 2012 and had an on-off relationship until early 2013, when it was confirmed they are definitely very much back on.
"I don't feel like I'm in a celebrity relationship," said John in 2013. "For the first time in my life I don't. I'm not in a high-profile… I know it's high-profile but it's hard to explain, it doesn't feel that way to me. And great, I'm glad."
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Celebrity splits of 2014 in pictures:
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