Hard-driving “Titanic” director JAMES CAMERON – whose near-maniacal obsession with promoting the 3-D release of his smash flick included a dangerous dive to the ocean’s deepest spot in an experimental submarine – got his head held underwater by star LEONARDO DICAPRIO, who drowned Cameron’s plea to star in a PR press tour!

“Cameron called DiCaprio earlier this year, telling him that if he went out to promote ‘Titanic,’ it could add up to $30 million in box office – and Leo would be paid handsomely for doing it,” said My Deep Sea Spy.

“But Leo declined, mostly because he’s still angry that Cameron lobbied like crazy for co-star KATE WINSLET’s Oscar nomination, while Leo got snubbed.

"He doesn’t look back on ‘Titanic’ very fondly.”