Looking for my grandmother's father: HEINRICH HORN of Schonberg, Mecklenburg-Strelitz, Germany.?

He was "a man of portfolio". I have a snap of him in military uniform taken at Altona Military Barracks, Hamburg. Great Grandmother born 1875 & he looks about that age. Family legend is that "he was the son of Duke George of Mecklenburg-Strelitz" (ie: G.D. Adolf Friedrich V). Thanks for any help.