It's ironic, really. But when James Cameron's romantic disaster classic Titanic held its world premiere in November 1997, studio bosses were worried it might sink without trace - as it was hitting cinemas at the same time as classics including Tomorrow Never Dies, Flubber and, er, Mortal Kombat: Annihilation.

How wrong they were. The film would go on to become the most successful movie of the 20th century - winning a staggering 11 Academy Awards (tying it with All About Eve and Lord of the Rings: Return of the King) and earning more than $2 billion at the box office.

Moreover, it also kickstarted the careers of Leonardo DiCaprio and Kate Winslet. And let's face it, the world would be a poorer place without Leo's endless quest for an Oscar and Kate's brutal honesty.

And so, as Titanic turns 18 years old, here are 18 facts about the movie that - like an enormous iceberg of trivia - you probably weren't aware of...

1. It's a James Cameron movie with a difference

Titanic is the only James Cameron movie that doesn't include or mention nuclear weapons.

2. Leonardo DiCaprio nearly didn't play Jack Dawson

Remember Elton from Clueless and Billy Chenowith in Six Feet Under? Yes, Jeremy Sisto was in the running to play Jack Dawson before Leonardo DiCaprio landed the role. And we have video proof! Watch his screen test with Kate Winslet in the video below.

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Prior to that, early studio favourites for the lead roles were reportedly Matthew McConaughey and Gwyneth Paltrow, while everyone from Christian Bale to Claire Danes was linked to the project before Cameron eventually struck gold with Kate and Leo.

Although the director's luck ran out elsewhere: Robert De Niro was offered the role of Captain Smith, but was forced to turn it down due to a gastrointestinal infection at the time. In addition to that King Kong icon Fay Wray said no to playing the elderly rose saying it looked like a "tortuous experience".

3. There was a J Dawson on board the real Titanic

His name was Joseph Dawson and he worked shovelling coal in the ship's engine room. Joseph was one of the 1,500 passengers who went down with the vessel, and his gravestone can be found at the Fairview Lawn Cemetery in Halifax, Nova Scotia.

4. The cast and crew tripped out on angel dust

On the final night of shooting in Nova Scotia, one or more pranksters mixed PCP into the clam chowder served to the cast and crew. 80 people were sent to the hospital with hallucinations.

5. The actors hired for the engine room scenes were only 5 ft tall

Cameron used short people to make his already sizeable set look larger on screen.

6. Kate Winslet had one hell of an ice breaker for Leonardo DiCaprio

The first scene Winslet and DiCaprio shot together was the moment Rose strips and asks Jack to "draw me like one of your French girls". How did Winslet cut through any potential awkwardness with DiCaprio? She flashed him the first time they met...

7. Paint me like one of your French girls Jack James

That famous sketch of a naked Rose wearing the Heart of the Ocean diamond was actually drawn by James Cameron. The film's writer/director is left-handed so he flipped the film to match the right-handed DiCaprio.

8. Kate Winslet's nude sketch fetched $16,000 at auction

Cameron's topless drawing of Winslet was sold off in a movie memorabilia auction by Premiere Props in 2011.

9. Kate Winslet caught pneumonia on set

The leading lady was one of the few actors and crew members who didn't wear a wetsuit during filming. Consequently, she caught pneumonia because, despite the water being heated, it was still pumped in from the freezing cold Pacific Ocean.

10. Kate Winslet hates Celine Dion's 'My Heart Will Go On'

"I wish I could say, 'Oh listen, everybody! It's the Celine Dion song!' But I don't," Winslet said in 2012 to coincide with the film's re-release. "I just have to sit there, you know, kind of straight-faced with a massive internal eye roll... It haunts me."

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11. James Cameron wanted Enya but DIDN'T want Celine Dion

Yes, Irish warbler Enya was top choice to compose the music for the film. Cameron even went as far as using existing tracks on the temp score for his rough cut. When Enya turned down the gig, in stepped Cameron's Aliens composer James Horner.

The director initially objected to the inclusion of any songs in the film, but Horner and Will Jennings covertly recorded a demo version of 'My Heart Will Go On' with Celine Dion and it eventually received the Cameron seal of approval.

12. Lindsay Lohan was almost in it

The future wild child auditioned impressively to play Cora Cartmell and was reportedly Cameron's top choice. However, the role eventually went to Alexandrea Owens after Cameron thought Lohan's red hair would lead audiences to think her character was related to Rose.

13. The time on the clock in the final scene holds huge significance

As Rose is reunited with Jack the time on the giant clock behind him reads 2.20am. This is the exact time the Titanic slipped beneath the surface of the water on April 15, 1912.

14. "I'm the king of the world!" was improvised

The film's iconic line was unscripted, with DiCaprio saying it the first time he stood on the bow of the ship. Cameron kept the line in, and even yelled it from on-stage at the Academy Awards when he won the Best Picture Oscar.

20th Century Fox

15. Jack WASN'T able to climb onto the raft with Rose

There was plenty of room for Jack aboard the makeshift life raft with Rose, right? RIGHT? Well, yes, according to James Cameron, but the debate is over buoyancy and not space.

"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," he told IGN.

"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."

20th Century Fox

16. There was just a single change to the 2012 re-release of Titanic

George Lucas may like to tinker with his movies after the fact, but James Cameron isn't so fiddly. For the 2012 re-release of Titanic the only change (aside from the 3D conversion) was to the arrangement of a star constellation in the night sky.

Astrophysicist Neil deGrasse Tyson had been complaining for years that Cameron's depiction of the sky at around 4.20am on April 15, 1912 was way off the mark. He provided Cameron with a detailed map and the film was digitally altered for that scene.

17. A TERRIBLE alternate ending was filmed

Forget all about that emotional reunion between Jack and Rose on the Titanic's grand staircase. No - criminally, the film almost ended with this clunky stand-off between Bill Paxton's Brock and Gloria Stuart's elderly Rose as she drops the Heart of the Ocean diamond into the sea.

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18. Titanic 2 actually happened...

Despite the obvious limitations, there was a straight-to-video sequel made in 2010. And you'll never guess: it was AWFUL.

"On the 100th anniversary of the original voyage, a modern luxury liner christened Titanic 2, follows the path of its namesake," the synopsis reads. "But when a tsunami hurls an iceberg into the new ship's path, the passengers and crew must fight to avoid a similar fate."

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