Horn was placed in charge of the famous 1953 England–Hungary match at Wembley Stadium and is one of only four men to have refereed two European Champions' Cup finals, beginning with the 1957 final in the competition's second year. In the 1962 final against Benfica, Real Madrid player Ferenc Puskás was seen to throw something into the crowd. Ken Jones, an English journalist, later asked Horn why he had not cautioned Puskás. Horn replied: "What you don't know is that I threw my whistle at Puskás," Horn said. "It hit him in the ear." (It was the whistle that Puskás had thrown into the crowd). The next September Horn refereed the playoff of the 1962 Copa Libertadores Finals after the original two-legged tie ended in a draw.