The director says Jack, played by Leonardo DiCaprio in the film, was no fool to not save his own life but it was due to pure physics that he made the choice to save Rose, played by Kate Winslet, reported Daily Mail.
"Actually it's not a question of room, it's a question of buoyancy. When Jack puts Rose on the raft, he tries to get on the raft - he's not an idiot, he doesn't want to die - and the raft sinks; it kind of flips.
"And so it's clear that there's really only enough buoyancy available for one person. So he makes the decision to let her be that person," Cameron said.
"If he got on with her they'd both be half in and half out of the water, and they would have both died," he added.
The director was directly addressing recent speculation by "Titanic" fanatics, who set out to prove that faulty logic was at play when Jack didn't climb onto the raft with Rose.
A series of photographs which popped up on Tumblr and dozens of other pop culture sites, begins by showing an aerial view of the original raft, with Rose lying on it and Jack hanging on in the water.