The 'Roar' hitmaker- who was seen with a ring on her engagement finger earlier this month, sparking speculation she was set to wed again - reportedly called off her romance with the 36-year-old singer ''within the last few days'', sources told E! News.
It is unclear why the couple have separated, and neither of them have commented on the reports as yet.
Katy - who was previously married to Russell Brand - began dating John in summer 2012 and they split briefly last March before reconciling.
The pair recently recorded a duet, 'Who You Love', for John's latest album 'Paradise Valley' and Katy, 29, previously said she was thrilled to work with him because she was a fan of his even before they began dating.
She said: ''I've been a fan of John's for years before I got to actually kiss him.
''I've been such a fan, I think he's so incredibly talented and gifted and a genius songwriter. So to be a part of anything he was doing was just natural.''
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