A short proof of the non-biplanarity of $K_9$ Vol. 26, no. 1, pp. 75-80, 2022. Regular paper. Abstract Battle, Harary, and Kodama (1962) and independently Tutte (1963) proved that the complete graph with nine vertices is not biplanar. Aiming towards simplicity and brevity, in this note we provide a short proof of this claim.  This work is licensed under the terms of the CC-BY license. Submitted: November 2021. Reviewed: December 2021. Revised: December 2021. Accepted: January 2022. Final: February 2022. Published: March 2022. Communicated by Giuseppe Liotta article (PDF) BibTeX