It's hard to miss the twinkle in Shankar Mahadevan's eye when he talks of sharing the mic with his younger son, Shivam, for the first time in Rakeysh Omprakash Mehra's Mere Pyare Prime Minister.

"He has sung as a child [artiste] in films, but this movie marks his major break in mainstream cinema as an adult [playback singer]," says Mahadevan, quick to add that the decision to have the young singer lend his voice to Rezgaariyaan was taken at Mehra's behest.