He was born in to Alfred Horneff (1883-1960), a photographer for the and Lina (1892-1963), an elementary school teacher. He had three siblings, Frank (1915-1988), Gabriele (1922-2001) and Louise (1924-2013). Horneff grew up and was educated in Munich, before they immigrated to , after he graduated from college in 1941. Interested in stage play, Horneff got a small part in an independently produced Grade-B Western, but his show business career then crumbled due to lack of budgets. In 1940, he became a stage performer until 1942.