The decision to get Balasubramaniam was jointly taken by the composers, along with director Rohit Shetty and lead actor Shah Rukh Khan.
"We are big fans (of the singer) since many years. I asked Shah Rukh if we can do this, and he said, 'You can'. So we immediately got in touch with his manager in Chennai," Shekhar said here Wednesday at the music launch of the film.
"He is 67 years old, he has sung more than 37,000 songs and he sounds like a 20-year-old. He is unbelievable, one of the best experiences ever to work with a legend," he added.
Directed by Rohit Shetty, 'Chennai Express' also features Deepika Padukone. It is releasing on August 8.