London, England (CNN) -- It's been almost 400 years since his death, yet controversy still surrounds the works of William Shakespeare.
It's long been thought Shakespeare penned 38 plays, but some scholars argue there is a 39th -- "Double Falsehood."
While the existence of "Double Falsehood" has been known for some time, the debate over it has recently become more heated.
Last year, authoritative collection, Arden Shakespeare, included the play in its latest edition of the complete works, sparking more discussion among scholars.
"There's not beautiful poetry in it, but (there are) moments of real psychological insight," said Phil Willmott, who's currently directing "Double Falsehood" at London's Union Theatre. "Even if it's not by Shakespeare, it's by someone very clever and I'm prepared to believe that someone is Shakespeare."
It's been proved that Shakespeare wrote a play called "Cardenio" in 1613. The piece was written with a young collaborator, John Fletcher, and was performed several times. However, the manuscript for "Cardenio" has since been lost.
"Double Falsehood" is an 18th-century reconstruction of "Cardenio" and scholars are now arguing over how much of the play is by Shakespeare.
"When Shakespeareans sit down with this play, we strain to hear the parts that sound Shakespearean," said expert James Shapiro, a professor at Columbia University, New York.
But he says there are several elements in"Double Falsehood" that suggest a strong Shakespearean influence.
"Under the substructure of the 'Double Falsehood' are many lines which convince Shakespeareans that Shakespeare is there," he says.
"Where exactly we're not sure, but the intelligence, the language, the metaphor, the structure -- all owe something to Shakespeare."
Shapiro believes arguments over Shakespeare's works will continue with new information about the playwright continually being discovered.
"There are always discoveries with Shakespeare," he says. "For all we know, lying in someone's attic is a manuscript of 'Cardenio' that will revolutionize our understanding of late Shakespeare."
The Royal Shakespeare Company will stage its re-imagining of "Cardenio" in the spring.
"Double Falsehood" hasn't been staged for around 200 years. Willmott's production takes place under a railway arch at the Union Theatre, one of the smallest of London's fringe theatres. It holds only 50 seats and its troupe of actors is playing for love, rather than money.
Willmott has his own ideas about the origins of the play. He thinks it belongs to John Fletcher, but was written very much under the supervision of Shakespeare.
"One theory that interests me is that Shakespeare was handing over to John Fletcher to be the resident playwright of the company," he said. "I get a sense that Fletcher did most of it, and Shakespeare added a bit of depth to it. It's an older man handing on to a slightly younger man."