On 23 July 1914, the Austro-Hungarian Ambassador to Serbia Baron Wladimir Giesl (pictured) sent a coded telegram to the Austro-Hungarian Minister of Foreign Affairs Leopold Count Berchtold. In his telegram, Giesl confirms the delivery of the Austro-Hungarian ultimatum to Serbia.
Baron von Giesl to Count Berchtold. Belgrade, 23 July 1914.
Ultimatum to Servia.
Note in question presented to [Serbian Cabinet Minister] Herr Pacu at 18:00 this evening.
Source: 1919 Austro-Hungarian Red Book, with minor edits.