AceShowbiz -

Katy Perry reportedly has a love song specifically written for her fiance Russell Brand. The song is meant to be a surprise for the "Get Him to the Greek" actor and will be performed by her right after they exchange wedding vows later this year.

"Katy has written a love song for Russell," a source told Daily Star. "She's planning to sing it to him right after they exchange vows. She can't wait to see the look on his face. It's going to be the most emotional moment of her life."

The source explained more in further statement, "Katy's fallen head-over-heels for Russell and isn't afraid to show everyone her inner feelings. She thinks that the best way she can express herself is with romantic lyrics."

Katy Perry falls for Russell Brand after she received a touching message in a copy of his book which was signed specially for her. To Rolling Stone, she recalled, "Russell had a copy of his book in the car, and I was intrigued. I asked him to sign it, and when I got home I read what he wrote: 'You are a mermaid, and I am drowning'."

She was taken in by the funnyman's note and invited him to join her on vacation in Phuket, Thailand shortly afterwards. She stated, "When we met in the lounge (of the hotel), I was so nervous. It was the most nerve-wracking thing I've ever done! I realized this man knew what would make me happy. He was really watching, and listening, and paying attention."