The 28-year-old star, who has admitted that many of the songs in her new album "Prism" are about Brand, explained that "Grace Of God" chronicles the end of her marriage to the actor.
“That song is evident of how tough it really was at a certain point. I asked myself, ‘Do I want to endure? Should I continue living?’ All the songs are real-life moments,” she explained.
Perry added that she needed to pen her dark times into song because she can only write about her personal experiences.
“I can only write autobiographically. I put all the evidence in the music. I tell my fans if they want to know the real truth about stuff, just listen to the songs.”
In July, the "Roar" singer told Vogue she had not heard from Russell since he broke up with her via text message.
“He’s a very smart man, a magical man and I was in love with him when I married him. Let's just say I haven't heard from him since he texted me saying he was divorcing me December 31, 2011.”