According to The Sun, the I Kissed A Girl hitmaker started putting pen to paper when her romance with Brand hit the skids and friends of Katy have claimed that she's begun to write songs about her heartbreak.
A source revealed: "Ever since problems started to emerge, she penned her thoughts in a diary which she goes back to to draw upon for lyrics for her songs.
"She has always said that writing is almost a form of therapy for her and she would often be found in her dressing room on tour writing in her diary.
They added: "She spent a lot of time in Hawaii over Christmas writing lyrics to two of her latest tracks."
Russell may want to cover his ears as it's not the first time Perry has written about a break-up, with song Circle The Drain from her hit Teenage Dream album documenting the reason behind her split with Gym Class Heroes frontman, Travie McCoy - blaming his alleged drug use.
Brand announced he had filed for divorce from Katy last Friday (30th December) with reports suggesting the Get Him To The Greek actor could be in line to pocket half of the 27-year old's rumoured £45million fortune.