The 'One That Got Away' singer, who separated from Brand in December, refused to mislead fans by claiming that the track she wrote two years ago was related to their divorce.
"I wrote it two years ago, which is funny because everybody is like, 'God, it sounds so current'," she told MTV.
"Some people that I work with were like, 'You should just say you wrote it a couple of weeks ago'. I'm like, 'I'm not a douchebag, I'm going to tell the truth'.
"I wrote it two years ago when I was writing and recording Teenage Dream, [but] it didn't feel right on the record."
Perry previously admitted that she found it "so crazy" that 'Part of Me' had suddenly become relevant to her life.
"I always knew that 'Part of Me' was a special song," she said. "It feels like my life plays out with these songs... I guess the universe is kind of - we're kind of like, dancing together in some weird way."
> Katy Perry teases next album: "I want to get back to my roots"
Listen to Katy Perry's 'Part of Me' below: