"Roshan Seth has lately been doing very little acting work, and by choice. Besides 'Guru', he has not done a single Hindi film in ages, and certainly not a mainstream commercial film," said a source close to the project.
Kabir and Seth's association goes back a long way.
"Seth has done the voiceover for every single documentary that Kabir Khan has made. When Kabir turned feature film director with 'Kabul Express', he again went to Seth to do the voiceover," said the source.
"Now when there was an acting role in 'Ek Tha Tiger' which Kabir felt only Seth could do justice to, there was no way Seth could say no to the director," the source added.
Apparently most of Seth's scenes are with Salman.
"Salman and Seth, who belong to completely different schools of acting, hit off beautifully. The vibes will show on screen," the source added.
However, Kabir remained unavailable for comment.