Mucha, Erté, and Vrubel, there were also illustrations by a famous-ish English artist.
George Sheringham (1884-1937) was best known as a stage designer, but he also illustrated books by the likes of Max Beerbohm, Arthur Conan Doyle, Cyrus MacMillan, and - it so happens - Edmond Rostand.
This edition of La Princesse Lointaine was published in 1919 and featured 26 illustrations by Sheringham. It was a limited run of 100 copies and was printed by J. Meynial, 'Aux dépens d'un Amateur' named Eugène Renevey.
Sheringham was evidently well qualified to take on the Rudel legend: he spent the final five years of his life as an invalid, though not from pining for an idealised woman, lointaine or otherwise.
The edition sometimes comes up on rare book websites (from where I sourced most of the pics).