By P. G. Wodehouse from the play Kleine Komedie by Siegfried Geyer.
I don't have much information on this, only what I can glean from a brief review (
Time, October 1929). It appears to be a pretty standard plot of a maid pretending to be a lady, a Prince posing as his valet and the valet pretending to be the Prince. The first production starred Gertrude Lawrence and Leslie Howard, both big names of the time. Ms Lawrence had already starred in
Oh Kay! and knew PG. Leslie Howard is known for many film performances (including
Gone with the Wind) before his disappearance in WW2.
According to PG in Author! Author!, the play was performed in Baltimore before Broadway [presumably as a try-out].