Hi,
if it´s a catholic chaplin it can´t be Wilhelm Prince of Prussia, who died of his wounds sustained during fighting in Valenciennes on the 26th May 1940 in a hospital in the Belgian city of Nivelles. He was protestant. So the remaining German nobility in the rank of kings came from Saxony, Bavaria and Württemberg. Whereas Saxony and Bavaria were ruled by catholic nobility, the house of Württemberg had a protestant and a catholic branch. And they took up the title of "Duke" after 1918.
After the death of the Prussian prince Hitler prohibited nobility of former reigning houses to be active in front duty and from 1943 to be active in the Wehrmacht at all (Prinzenerlass). So if this is a photo of a Prince´s funeral near the front, it must have been taken before May 1940.
If the crown was used for princes from other houses as the above more would qualify, like e.g.:
Heinrich Prinz zu Sayn-Wittgenstein-Sayn, a pilot shot down in 1944.
GreyC