It went on to win the Oscar for Best Song and cover versions by Frank Sinatra, Ella Fitzgerald, Doris Day and Tony Bennett enchanted audiences worldwide.

Pop star Ariana Grande even recorded it as a single in 2017 to benefit survivors of the Manchester Arena terror attack that killed 22 people.

But Tinseltown is now in turmoil over claims the poignant ballad – composed in 1938 by Harold Arlen and lyricist Yip Harburg – may have been plagiarised from a long-forgotten piece of classical music written 28 years earlier in 1910.

The composition, Concert Étude, Opus 38, bears “striking similarities” to Over the Rainbow, according to Norwegian concert pianist Rune Alver.

He discovered it in a music archive in Bergen and said: “There is no debate about it – of course it is plagiarism.”

Opus 38 was written by Scandinavian composer Signe Lund, who copyrighted it in Chicago during one of her many visits to the US, several of which coincided with Mr Arlen’s early years as a music student.

Ms Lund’s work later fell into obscurity after she was ostracised for being a Nazi sympathiser during the Second World War, and she died aged 81 in 1950.

The rediscovery of her work has triggered a debate in Hollywood over the legitimacy of Over the Rainbow’s Oscar win, with even Mr Arlen’s son Sam, who runs his estate, admitting “there’s no question” about the similarities between both pieces of music.

He added: “You hear it, certainly. Whether it was intentional, no one knows. It’s all conjecture.”

Theatrical composer Stephen Schwartz, whose Broadway hits include the score of Wicked, the Wizard of Oz prequel, said: “Of course I can hear the similarity.

“I’d say it’s a coincidence, or maybe something Arlen heard or played when he was young and it just became part of the palette from which he drew.”