Katy Perry had been having doubts about her relationship with John Mayer ''for some time'' before they split.

The 'Dark Horse' singer reportedly called time on her 18-month romance with the 'Gravity' hitmaker last week but an insider says the decision had been a long time coming.

The source told E! News that Katy, 29, felt there were ''certain differences in their personalities'' and she felt she and John, 36, were ''not right for each other'' but she took some time to ''acknowledge'' her instincts and end the relationship.

According to the source, Katy is said to be ''relieved'' the romance is over and is ready to move on with her life.

The pop star - who was previously married to Russell Brand - is currently in Australia and brushed off questions about her relationship status during a TV interview earlier this week.

While appearing on 'Sunrise', fans outside the studio were able to ask Katy questions, with one enquiring: ''We were just wondering if you have a boyfriend.''

The 'Roar' hitmaker laughed and replied: ''If I have a boyfriend!? All of my fans are my boyfriend!''

She then leaned over to a koala bear seated in the studio with her and said: ''This is my boyfriend! See!''