Davy Jones' double was played by future "Rodney on the ROQ" radio host, Rodney Bingenheimer. A photo by Henry Diltz shows them facing each other in costume.
The Courtier and Michael are seen wearing exactly the same blue robes. In The Squire of Gothos (1967), William Campbell can also be seen wearing the same coat as Trelane. 'The Squire of Gothos' was filmed in October/November 1966; "The Prince and the Paupers" that December.
The first episode where a Monkee plays a dual role.