Performed by Anushka Sharma's character Rosie and sung by Neeti Mohan, the song comes at a crucial moment in the movie.
During the musical event last night, the director explained the history behind the number.
"'Sylvia' was the name of Nanavati's wife. The song is inspired by the tabloid perception of the story," said Kashyap.
KM Nanavati vs State of Maharashtra was a 1959 Indian court case where Kawas Manekshaw Nanavati, a Naval Commander, was tried for the murder of Prem Ahuja, his wife's lover.
The Nanavati case was also India's first 'media trial', provoked by a highly charged and often biased coverage by the tabloids of that time.
Earlier, in an interview to PTI the director revealed his struggle to bring the story on the big screen and how they managed to finally scale it down. Still "Bombay Velvet" is Kashyap's most expensive film till date.
"When we were planning to make the film in 2009 with Aamir, the budget was coming around Rs 160 crores. It was not even feasible because films were not earning that much. We scaled the cost down," Kashyap said.
The film's delay generated some bad publicity but Kashyap is confident that once people watch it, they will love the world that has been created on the screen. "It is Ranbir's best work. For the first time his father loved any of his films while his mother hugged me and told me that this brings the best in her son."
Ranbir said the film was not even offered to him, he called up the director because it is rare to be a part of something like this.
There are references of that era, be it a Cary Grant picture hanging in Johnny Balraj's club or the scene where Ranbir comes out holding guns in both hands, a la Tony Montana of "Scarface".
"There are many such references because both Anurag and I are fans of that world, Martin Scorsese, Al Pacino. These little references are our tribute," Ranbir said.