Katy Perry reportedly finished with John Mayer after hearing rumours that he'd been unfaithful.

It was believed the pair were on the verge of marrying before reports of a split surfaced at the end of February.

And now sources say that it was the constant gossip surrounding John's commitment to Katy that eventually caused the separation.

"Katy has always been concerned about John's infidelities. And I guess she was right, he does have a womanising reputation. He's apparently been seeing girls in a number of different cities and he's even rumoured to have a secret girlfriend in San Diego who flies to see him whenever Katy is away," an insider divulged to British magazine Grazia.

"It seems Katy heard the rumours and pulled the plug, but friends are concerned it's worse than she knows."

John, who has been dubbed Mayer the Player by some media outlets, is said to have had texts from "from some random girl" on his phone.

The insider says this is just the "tip of the iceberg" though.

Katy, 29, was spotted wearing a ring on her wedding finger weeks before news broke of her and John's separation.

The Firework singer hasn't had time to dwell on her love life though as she's busy with the promotion of her Prismatic tour.

She stopped by Australia last week, and while she's yet to comment on John, she did bombard her Australian fans with a series of tweets.

"Thanks for the love, Aussies! (sic)," she gushed.

Meanwhile John has been pictured out with a mystery brunette in LA.