Why Jack had to die in Titanic

Leonardo DiCaprio's death in Titanic is one of cinema's biggest upsets. Photo / Supplied

It's the movie ending that sparked a thousand theories — why did Jack Dawson have to die at the end of Titanic?

For those who haven't seen Titanic (and have been living under a rock) Jack — played by Leonardo DiCaprio — dies by freezing in the Atlantic Ocean after the ship sinks, while Rose (Kate Winslet) manages to survive by staying out of the water on a floating piece of debris.

The ending to one of cinema's greatest romances has left fans frustrated for more than two decades.

Why couldn't Jack fit on the door? Why didn't Rose make room for him instead of hogging all the space?

But it wasn't as simple as that, according to Titanic's director James Cameron. He told 60 Minutes that it was "fundamental" that Jack die for the plot to make sense.

"It had to have a tragic, bittersweet ending," Cameron said. "I mean to me a love story is a transfer of energy, sometimes bi-directional. In this case it was a transfer of energy from his life force to her."

Cameron argued that instead Jack gave Rose "that spark she needed to survive" and "showed her another way of living".

"The promise that she would never let go is the promise to never let go of life," he said.

"The irony is she had to let go of his hand and let him go, but she never let go of what he had given her, which is that gift and that spark.

"So yeah Jack had to die, that was kind of fundamental."

Cameron told Vanity Fair in 2017 that his decision to have Jack die had been an "artistic choice" and it was "silly" to still be having this discussion 20 years on.

"Had he lived, the ending of the film would have been meaningless," he said.