The regimental owner of the 16th hussars was Field Marshal Alexander Üxküll Gyllenband until 1916. After the accession of Emperor and King Charles to the throne, the owner of the regiment became the spouse of the new ruler, Zita.The change was recorded by the regiment on several cap badges.
Among them is the Z monogrammed oval badge. Charles often pinned cap badges to his hat. Usually the badge belonged to the unit he just visited. According to the caption of this picture, he is visiting here the Karst Plateu after the 11th Battle of Isonzó, i.e. in September 1917. As far as I know, the 16th Hussars were not here at that time, so it is a bit strange that the ruler wears this Kappenabzeichen.