Tsar Alexander I died far away from St Petersburg so his coffin was closed on arrival. After his death stories appeared that he had not died but become a monk or hermit.
King Willem II died in 1849 but after his death some rumours went about that he lived on as general Totleben (in German a translation of Deadliving) in Russia.
Another famous case what that of the Dunkelgrafin who was said to have been Madame Royale and having been exchanged for another girl during the trip from Paris to Vienna after she left the Temple.
In Russia several men claimed to be dead Tsars. There were two false Dimitri's and Peter III.
In most cases it is very clear we are faced with imposters. Nauendorf, the false Dimitri's and Peters, the Dunkelgrafin, Anna Anderson and several others claiming to be members of Nicholas II's family are all proven to have been imposters.
Some time ago, I posted on the subject of royal disappearances, faked deaths, and cover-ups (which almost inevitably lead to conspiracy theories, not to mention appearances of imposters). Famous examples include the princes in the tower of London, the lost dauphin of France, Anastasia/Anna Anderson, and Kaspar Hauser.
Until recently, I didn't know that King Ludwig II of Bavaria could also be added to the list. But according to a documentary, there is a popular (if not prevalent) urban legend, according to which "Mad" Ludwig did not actually die on the fateful night of June 13, 1886. That he actually managed to escape confinement at Schloss Berg by swimming to freedom, and that the body inside his coffin is actually a wax double!
Anyhow, bearing this in mind, I was wondering if there are other examples of royal coffins whose contents have been questioned -- suspected of being empty or containing dummies, or possibly of other people's corpses.