India, April 28 -- Sonu Nigam and his sister, Teesha Nigam, recently collaborated for a single, Humnava. This marks the singers' fifth musical outing together. "It's always special to sing a duet with your little sister," says Sonu, as Teesha adds, "Apart from being my brother, he is the greatest singer alive. So, it's always an honour to be his co-singer."...