The central plot twist of "Titanic" isn't a surprise event, as the audience knows from the outset that the ship will sink. The true narrative suspense lies in the fate of its fictional protagonists, Jack and Rose. The film meticulously builds their forbidden romance, making the audience invest deeply in their survival as a couple.
The film's most devastating turn is the death of Jack Dawson. After the ship sinks, he secures a floating piece of wreckage for Rose but remains in the freezing water himself. He dies of hypothermia, his ultimate sacrifice allowing Rose to survive. This moment is the emotional core of the film's tragedy, revealing that while their love was powerful enough to break social barriers, it could not overcome the cruel randomness of fate and the laws of physics. Rose, upon being rescued, takes on his last name, 'Dawson', effectively erasing her old identity and starting a new life built on the freedom he showed her.
The story's final reveal comes in the present-day narrative. The elderly Rose, after finishing her story, walks to the stern of the research vessel. It is revealed that she has possessed the 'Heart of the Ocean' diamond all along, having found it in Cal's coat pocket after being rescued. She drops the priceless jewel into the ocean, a symbolic gesture of returning it to the site of her true love's resting place. The film concludes with a shot of the elderly Rose in her bed, surrounded by photographs of a long, adventurous life—proof that she kept her promise to Jack. The camera then fades into a final, dreamlike sequence where a young Rose walks up the Grand Staircase of the restored Titanic, greeted by all who died, and finally reunites with Jack. This ambiguous ending can be read as her peaceful death and reunion with him in the afterlife, providing a poignant and spiritually fulfilling conclusion to their epic love story.