In the summer of 1966, when I was a second year undergraduate at Cambridge, Alfred Hitchcock came to give a question and answer session in the Lady Mitchell Hall, and to screen his “favourite film” Shadow of a Doubt (1943) – the one about the Merry Widow serial killer.

Hitchcock walked away a little, turned his head and with a deadpan expression said: ‘Sunrise’

This was shortly after his epic 25 hours of interviews with François Truffaut had been published in France, and the year before they were published in English. Hitchcock was already the best-known and most recognisable film director in the history of movies. After the session, I found myself, for a few seconds, face to face with him. There he was, dressed in trademark plain dark-blue suit, crisp white shirt, dark silk tie, with a creased copy of the Times poking out of his jacket pocket.

Close-up, he looked apprehensive, ill at ease, with a complexion rather like the colour of the Financial Times – surrounded as he was by an excited flurry of young cineastes waving programmes for him to sign. Tongue-tied, for some instinctual reason I hummed aloud the opening bars of the signature tune of his long-running TV show The Alfred Hitchcock Hour – pom/pom-pom-pom-pom/pom-pom-pom – Charles Gounod’s jolly-macabre Funeral March of a Marionette, written in 1872. For the show, it had been wittily rearranged for eight bassoons.

Hitchcock smiled, walked away a little, turned his head and with a deadpan expression said one word: “Sunrise…” I hadn’t a clue what he meant by this. It was like “Rosebud…” from Citizen Kane, I supposed. But the great man had actually spoken to me. The last I saw of him was as he made his way through the crowd for his waiting Rolls in Sidgwick Avenue.

About 40 years later, someone sent me a DVD of FW Murnau’s film Sunrise (1927), with its original score restored, and the mystery was at last solved. The sequence in Sunrise where the peasant couple visit a photographer’s studio in the city – and accidentally knock over a headless Winged Victory sculpture, one of the photographer’s props – was accompanied by Gounod’s funeral march, the same tune with the same macabre charm as Hitchcock’s signature.

He was trying to let me know – with a characteristically mysterious flourish – that Sunrise was where he’d found the music, that a distant memory of Murnau’s film had originally inspired him. It had taken me 40 years to understand why he’d used the S word.

Many of Alfred Hitchcock’s films were influenced by the techniques of silent cinema – and by German expressionism: he’d even observed Murnau at work in Berlin in 1924 – so it figured, as I realised in retrospect.

My one-word conversation with the great Alfred Hitchcock.

Christopher Frayling’s latest book, Frankenstein: The First Two Hundred Years, is published by Reel Art Press, £29.95. Order a copy for £25.46 at bookshop.theguardian.com