Director Ang Lee attends the opening night gala presentation of his film ''Life Of Pi'' at the 50th New York Film Festival at Alice Tully Hall in New York September 28, 2012. [Photo/Agencies]

Despite the slick special effects, creation of a fake tiger and shooting underwater, the toughest part of making "Life of Pi" was telling the story, director Ang Lee said Monday.

The Academy Award-winning director who is in Mumbai to promote his latest project, based on the bestselling novel of the same name, said it was the hardest movie he had ever shot.

"The book makes a philosophical point about theology and zoology. It examines illusions. To me that is the hardest. How do you create illusion, especially with so much money?" Lee said at a press conference in Mumbai.

"I'll be honest with you, I have been very stressed for the last four years,".

The film, a fantasy tale about a boy stranded in the middle of the ocean in a boat with a tiger, has had encouraging early reviews, with "The Hollywood Reporter" calling it "exceptionally beautiful".

The largely Indian cast, including lead actor Suraj Sharma, who Lee picked out of 3,000 teenagers, and the Indian setting of the film is likely to appeal to Indian movie-goers, now increasingly enamored with Hollywood.

Lee and his cast are kicking off international promotions for the film in India.

"The universal theme of us touching God is spiritual and India is a spiritual place," Lee said.

"To me it was a profound experience, but on the surface it has to be fun, adventurous and illusive."

The film, which will be released worldwide on November 23, will also open the International Film Festival of India on November 20th.