Director Yash Chopra plans to keep the climax a secret for as long as possible from audiences as well as the cast, Mumbai Mirror claims.
"Which one of the two ladies finally gets the guy is not known to anyone except Yashji and Aditya Chopra. Even Shah Rukh Khan, who's very close to him, has not been told," said a production source.
The 79-year-old filmmaker is expected to begin shooting the first UK schedule of the production within the next few weeks.
"It's a love triangle set in London, where the three actors play contemporary working-class characters. The treatment of love is very mature," added the source.
"Katrina is not the 'looker' and Anushka the 'actor' in the script. Katrina has one of the most challenging roles of her career."
The film's soundtrack has been composed by award-winning music director AR Rahman.