While their relationship began with the fire that broke out on the sets of the 1957 film Mother India, it was while recuperating from the injuries that the two really came close, says author Kishwar Desai in her book Darlingji - 'the true love story of Nargis and Sunil Dutt.
"If it were not for him, perhaps I would have ended my life before the 8th of March. For I alone know the turmoil that was going through me. 'I want you to live,' he said and I felt I had to live. Begin all over again", Desai quotes Nargis from her personal diary written after the accident.
Sunil was a man who treated her 'like a normal human being' and in rescuing her from the accidental flames, was perhaps the first person in a long time to have really done something for her.
"As she sat by his bedside, she realized that his courage in pulling her out of the fire had impressed her. It was a long time since someone had sacrificed anything for her.
She was the one who always did things for others, whether it was for her family or Raj...." writes the author on what drew Nargis towards the handsome Dutt.
Struggling to come out of a futile relationship and dealing with a family which in her own words considered her a mere 'money-making machine', Nargis confided in her new found love, laying her past thread-bare in front of him.
"She said she was 'shameless' in discussing every detail of her life, and was not worried because she knew 'that his shoulders were always there for me to cry on- and I also knew that his garments will absorb my tears and not scatter them out for people to make fun of me'," the book quotes her diary.
Raj Kapoor, with whom Nargis worked in as many as 16 films, six of which were RK banner productions, was undoubtedly the first love of her life.
However, Sunil Dutt came into her life when her first relationship had run into a cul-de-sac, leaving her shattered, says the book compairing her bonding with the two men.
According to Desai, "Raj had come into her life when she was 19 and ready for a relationship. If it hadn't been Raj, it would have been someone else; he just happened to be her first boyfriend."
Nargis later realized she was uselessly clinging to a one-sided relationship and that despite showing an inclination towards her, Raj, who was a married man, would never respond to her.
"She confessed to Sunil that her relations with Raj had been on a 'razor's edge' and that she had been desperately trying to cling to him without any response. She told him that Raj 'had started making feel disgusting even to myself' and that before she met Sunil, she had 'no reason to be living'", writes Desai.
Though in complete awe of the then leading lady of Indian cinema, Sunil Dutt, who as a newcomer had fallen for Nargis, was still intimidated by her star status and feared it could impede the future of their relationship.
The difference in their status was vast. While Sunil received a monthly amount of ten or twelve rupees working on Mother India, Nargis was reportedly offered a total sum Rs 50,000. Moreover, Nargis was already honoured with the Padma Shri, while Sunil was still struggling to find feet in the industry.
Sunil's insecurity was compounding by the stories doing the rounds in the industry, thanks to the gossip- mongers.
"Sunil was a victim of a callous film-industry.... he was both an object of envy - for being involved with the glamorous screen siren Nargis- and scorn because people thought he was trying to use her to push her own career forward", says the author, who has drawn heavily from the diaries and letters of the Dutt family.
"And then of course, there was the niggling issue of Raj: Nargis was not an easy woman to love, she came with too much baggage, and at times he could not cope with it" she adds.
The book that gives a parallel track of the lives of the Dutt duo, also gives an insight into the equation Nargis had with Raj Kapoor.
Deeply involved with the 'blue-eyed actor', Nargis had almost become a part of the R K banner and stopped working outside it, an issue that was a major point of contention between her and her family.
Determined that she would never spoil Raj's family life, Nargis still sought out ways to fructify her relationship with him.
In a bid to find a way out, she even met Morarji Desai, who had just worked on the Hindu marriage laws, hoping that he would be able to guide her. But their meeting was a disappointment and nothing was resolved.
As opposed to Raj Kapoor, Sunil turned out to be a pillar of strength to Nargis, giving her the respect she was worthy of.
"Sunil's shy and gentle style, quite unlike Raj's flirtatiousness was like a balm to her. Unusually, she was spending time with a man who treated her like a normal human being", writes Desai.
Though love bloomed between the pair during the making of Mother India, it was only after the film's release and subsequent success that the two became public with the relationship.
"Her fame was the problem he was struggling with. He wished she was an ordinary woman, and not a star; for him she was simply the woman he loved. But he could not talk about their love, for there were many who would be against their relationship", she writes.
Moreover, Mehboob Khan, director of the film was apprehensive that the film's commercial prospects might suffer, if the onscreen mother-son duo flaunted a romantic relationship in full media glare, writes the author.