Cardenio is considered a lost play. The authors are believed to be John Fletcher and William Shakespeare. The attribution is based primarily upon two 1613 performances by the King’s Men acting troupe of a play listed by either the title Cardenno or Cardenna. Another clue to the existence of the play is a 1653 entry in the Stationers’ Register which credits the work to “Mr. Fletcher and Shakespeare.”
That same year publisher and collector of manuscripts Humphrey Moseley attempted to establish copyright on a play titled The History of Cardennio by Shakespeare and John Fletcher. That manuscript at some point went missing is assumed to be lost. Lewis Theobald produced a play titled Double Falsehood in 1727 that he asserted to be an adaptation of an un-produced Shakespeare manuscript and which features a hero named Cardenio. Again, the manuscripts for this play have never been located, but contemporary accounts of the productions have raised questions among theatrical scholars regarding its peculiar lack of Shakespearean qualities.
Until a verified original or copy of any of these versions is discovered, Cardenio appears to go down in history as yet another mystery revolving around Shakespearian authorship.