In the 1920s, the now mature Wallis began to play character parts, appearing with great success as Louis XV in Madame Pompadour (1923) by Leo Fall, Frederick Lonsdale and Harry Graham, starring with Evelyn Laye and Derek Oldham.
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Collaborating again with Courtneidge, he adapted the composer Leo Fall's operetta Der liebe Augustin as Princess Caprice (1912, Shaftesbury).
He was supposed to enter the engineering profession, but his acquaintance with Leo Fall led him to study music at the Vienna Conservatory, where he studied composition under Robert Fuchs, and became educated as a piano teacher and Kapellmeister.
Willner and Fritz Grünbaum (after a comedy by Gatti-Trotha), adapted into English by Basil Hood (from the 1907 Die Dollarprinzessin), with music by Leo Fall and lyrics by Adrian Ross.