Amitabh Bachchan and Ranbir Kapoor sharing screen space was already a treat for their fans and now the makers of ‘Brahmastra’ are planning to shoot a song featuring the two. Buzz suggests that this peppy dance number will be choreographed by Farah Khan. Ranbir and Big B have already started preparing for their dance, while the song will be canned in Mumbai. ‘Brahmastra’ is the first in a trilogy of super-hero films, directed by Ayan Mukerji. The film features alleged real life couple Ranbir Kapoor and Alia Bhatt, while ‘Gold’ actress Mouni Roy plays the villain. ‘Brahmastra’ is scheduled to hit the screens in Christmas this year.