Image copyright Paramount/Millennium Films Image caption The Legend of Hercules was released six months before the Dwayne Johnson version

Sometimes a story is so good, you just have to tell it twice.

This seems to be particularly true in Hollywood, the landscape of which is littered with examples of "twin films" - two movies that are not only about the same thing, but are often released around the same time.

The Mercy, which came out in February and starred Colin Firth, told the true story of Donald Crowhurst, an amateur British sailor who joined a round-the-world yacht race in 1968.

Literally out of his depth, he attempted to cheat using falsified navigation logs before mysteriously disappearing from his vessel.

The story was so extraordinary that two different directors - James Marsh and Simon Rumley - thought it worth making a film about. So both did.

StudioCanal, who already had Firth's film in development, avoided a slightly awkward situation by buying the rights to the other one as well.

"It's a bit of a unique situation," said Mike Riley, producer of Rumley's Crowhurst. "There's two films - two very different films - about the same thing."

Except it's not unique at all. In fact, it happens surprisingly frequently.

Image copyright StudioCanal Image caption Spot the difference: Colin Firth in The Mercy and Justin Salinger in Crowhurst

Keith Simanton, senior film editor at IMDb, says that twin films often come about because of genuine coincidence.

"I bet if you went out right now you could find two, three or more scripts which are about the same thing and haven't been made," he tells BBC News.

"For example, we went a long stretch without any movies about Dunkirk. Yet in 2017 we had two major features about it - Darkest Hour and Dunkirk.

"Then there are instances where creative types get put together and they click, and even though the exact movie they coalesced for doesn't get made, they stick together and make something vaguely familiar.

"For example, Mark Wahlberg and Will Ferrell were brought together for the action-buddy cop flick that eventually became Cop Out. They ended up not starring in that film but moved on to a different studio with a different script, but with the same feeling, called The Other Guys."

According to Simanton, though, one of the most frequent reasons for the twin film phenomenon is what he calls "first to market".

"For example, a studio knows Dwayne Johnson is making a Hercules movie, and they go 'Hey, we have the rights to this other script to another Hercules movie, and the legend of Hercules is in the public domain.'

"'Wouldn't it be great if we could get ours out before they do?'"

Image copyright Warner / Columbia Image caption Cop Out and The Other Guys were both released in 2010

Ironically, though, being last to market with an idea is sometimes the best bet. This happened in the late 1980s when a plethora of films about age-switching were released.

"First there was Like Father Like Son, starring Dudley Moore, then Vice Versa with Judge Reinhold, and then 18 Again with George Burns," Simanton says.

"The last to come out was Big, starring Tom Hanks. And that's the one that made over $100m [£71m] at the box office, and Penny Marshall became the first woman director to achieve that milestone.

"Theoretically, Big shouldn't have made any money. There had been three others that had come out before it with basically the same idea, but the last one was the best."

Here are some few more examples of so-called "twin films" that came out eerily close to each other.

Olympus Has Fallen & White House Down

Image copyright Columbia / Millennium Films

Storyline: Action thrillers that see the US president's safety at risk from terrorists attacking the White House.

Stars: Gerard Butler and Aaron Eckhart in Olympus Has Fallen; Channing Tatum and Jamie Foxx in White House Down.

Release dates: March 2013 for Olympus, followed by White House Down three months later.

Box office: $170m (£120m) for Olympus Has Fallen; $205m (£146m) for White House Down.

Trivia: Despite White House Down being more successful at the box office, it was Olympus Has Fallen that sparked not one but two sequels.

Butler and Eckhart reprised their roles in 2016's London Has Fallen, while a third instalment, Angel Has Fallen, is due to be released next year.

No Strings Attached & Friends With Benefits

Image copyright Paramount / Castle Rock

Storyline: Two friends, both single, hook up for casual sex without the complications of an actual relationship.

Release dates: January 2011 for Strings, with Benefits coming out the following July.

Stars: Ashton Kutcher and Natalie Portman in No Strings Attached; Justin Timberlake and Mila Kunis in Friends With Benefits.

Box office: Incredibly, both took almost exactly the same amount - around $149m (£106m).

Trivia: The two films' female stars appeared with each other in Black Swan the year before these two films were released.

Antz & A Bug's Life

Image copyright Dreamworks / Disney Pixar

Storyline: Computer-animated children's films that focus on the lives and ecosystems of tiny insects.

Stars: The voices of Woody Allen and Sharon Stone in Antz; the voices of Kevin Spacey and Julia Louis-Dreyfus in A Bug's Life.

Release dates: October 1998 for Antz, with Bugs following just one month later.

Box office: $171m (£121m) for Antz; $363m (£258m) for A Bug's Life.

Trivia: For two family-friendly films, there was a distinctly unfriendly feud happening behind the scenes.

A row broke out between Pixar bosses Steve Jobs and John Lasseter and DreamWorks CEO Jeffrey Katzenberg, who had left Disney's film division to set up a rival company.

Jobs and Lasseter claimed Katzenberg had stolen their idea, which Katzenberg denied. The press revelled in how dirty the fighting got, with Katzenberg bringing forward the release date for Antz by six months to beat A Bug's Life into cinemas.

Antz was a box office success, but it didn't harm the Pixar film which eventually made more than twice as much as its rival did.

Marguerite & Florence Foster Jenkins

Image copyright CNC/Pathe

Storyline: A socialite who fancies herself as a successful singer embarks on a music career. Unfortunately, she's tone deaf.

Both films - one French, the other English-language - are based on the real-life story of Florence Foster Jenkins (1868-1944).

Stars: Catherine Frot and Andre Marcon in Marguerite; Meryl Streep and Hugh Grant in Florence Foster Jenkins.

Release dates: September 2015 for Marguerite, with Florence Foster Jenkins following in May 2016.

Box office: $497,000 (£354,000) for Marguerite; a slightly higher $49m (£35m) for Florence Foster Jenkins.

Trivia: "One month before the shooting of Marguerite, I heard about [Florence Foster Jenkins]," said French writer-director Xavier Giannoli in March 2016. "For me, it was terrible."

Deep Impact & Armageddon

Image copyright Paramount / Touchstone

Storyline: A comet/asteroid is hurtling towards Earth at an alarming rate, threatening the existence of the human race.

Stars: Robert Duvall and Morgan Freeman in Deep Impact; Bruce Willis and Ben Affleck in Armageddon.

Release dates: Just two months apart - May 1998 for Deep Impact, and July 1998 for Armageddon.

Box office: $349m (£248m) for Deep Impact; $553m (£394m) for Armageddon.

Trivia: The duelling films were referenced by an episode of Friends, one of the biggest shows on TV at the time.

"Which one was Deep Impact and which one was Armageddon?" Chandler asks Monica while struggling to get to sleep one night.

"Deep Impact was the one with Robert Duvall," she replies. "Armageddon is what's going to happen to you if you wake me up."

Capote & Infamous

Image copyright Sony Pictures / Warner

Storyline: Another real-life tale of what happened when writer Truman Capote investigated the murder of a Kansas family alongside his childhood friend, aspiring novelist Harper Lee.

Stars: Philip Seymour Hoffman and Catherine Keener in Capote; Toby Jones and Sandra Bullock in Infamous.

Release dates: February 2006 for Capote; October 2006 for Infamous.

Box office: $49m (£35m) for Capote; $2.6m (£1.8m) for Infamous.

Trivia: "Good news! I've finished my script," cried Infamous screenwriter Douglas McGrath over the phone to producer Bingham Ray in 2003.

"I know," replied Ray. "I've got it on my desk." McGrath responded: "Uh, no you don't, because I have it on my desk."

It turned out, as Ray later recalled to The New Yorker, he had in front of him a different script about the same period of Capote's life. Awkward...

Dante's Peak & Volcano

Image copyright Universal / Fox

Storyline: The eruption of a volcano threatens the life of locals.

Stars: Pierce Brosnan and Linda Hamilton in Dante's Peak; Tommy Lee Jones and Don Cheadle in Volcano.

Release dates: February 1997 for Dante's Peak; April 1997 for Volcano.

Box office: $178m (£127m) for Dante's Peak; $122m (£87m) for Volcano.

Trivia: Pierce Brosnan's character in the film shares a surname with Timothy Dalton, the actor he'd just taken over from as James Bond in real life.

Box office takings are worldwide figures taken from Box Office Mojo. Release dates refer to the earliest general public release date.

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