Besides being the host, Walt Disney was an actor in this episode (playing himself).
King Brian: Darby O'Gill. What class of deceitful trickery are you up to this time?
Darby O'Gill: Good evenin', Your Honor. I brought a Mr. Disney here to see you, sir.
King Brian: Disney? I know the Daleys, the Duffys, the Donovans, the Dedrens, the Doleys, the Dardys, but Disney? No. I don't know any Disneys. So, good night, sir.
Walt Disney: Some time ago, I decided to make an Irish picture. For Ireland is the home of the leprechaun. And the little people have always fascinated me.
Walt Disney: Well, I've always wanted to go to Ireland, so, what can I lose?
Pat O'Brien: Nothing but your heart.
The King Brian scenes are not done trough split image but a technique devised by Peter Ellenshaw called Forced Perspective. This is done by having King Brian four times farther away from the camera than Walt and Darby, making him look one quarter the size. The merge between the two is done with a mirror, with Walt and Darby appearing through a part of the mirror where the silver has been removed.
This episode is included on the DVD of Darby O'Gill and the Little People.
This episode was filmed at the Disney Studio in Burbank and not Ireland as stated by Walt in the episode.