Christopher Plummer probably remains best-known for his portrayal of Captain Von Trapp in the 1965 blockbuster The Sound of Music. While his character infamously appears rather grumpy on screen, behind the scenes the actor himself was also often in a difficult mood, and despised making the film.

Even in the 1960s, singing nuns and Nazis were somewhat kitsch, but the undeniable charm of Rodgers and Hammerstein’s musical melted the toughest hearts, except perhaps that of its leading man. It’s saying something if the perpetually cheerful Andrews had difficulty dealing with his on-set behaviour.

Despite the film’s immediate and ongoing extraordinary box office success, Plummer was already making those infamous ‘Sound of Mucus’ comments by the following year. And during filming, the actor resorted to drastic measures to get through scenes, including hitting the bottle before perhaps his most iconic and beloved one of all.

Plummer had a long and illustrious stage and Hollywood career and finally won an Oscar for Beginners in 2012. He made his Broadway debut in The Starless Sky in 1953 – a play that closed on its opening night. He was praised for sensitive and nuanced performances over the years, culminating in his final Oscar nomination in 2018 for All The Money In The World.

Many “serious” and non-singer actors found themselves performing in musicals during Hollywood’s Golden Age, including Marlon Brando in Guys And Dolls and Rex Harrison in My Fair Lady, but Plummer later admitted he behaved ungraciously while making The Sound of Music.

He said: “I was a pampered, arrogant, young bast**d spoiled by too many great theatre roles… Although we worked hard enough to make (Captain Von Trapp) interesting, it was a bit like flogging a dead horse. And the subject matter is not mine. I mean, it can’t appeal to every person in the world. It’s not my cup of tea.”

In his 2008 memoir, In Spite of Myself, the actor also candidly admitted: “I was drinking like mad at the time…”

The actor also later revealed on the 35th Anniversary DVD of The Sound of Music that his anxiety led him to indulge even more heavily. He confessed that he was completely drunk during the filming of the climactic music festival scene where the family performs Edelweiss before escaping into the mountains.

Plummer said: “I was shaking, I was terrified with a full orchestra the first time. Julie had to hold me, I would have fainted.”

Fortunately, like all accomplished actors, he managed to turn the moment into pure cinematic magic, with Captain Von Trapp captivating the festival audience, and millions of moviegoers, with his display of vulnerability and raw emotion.

Plummer had publicly laid the demons of The Sound of Music and that song to rest with an emotional Broadway surprise for Andrews on June 8, 1977, during her Victor Victoria closing night. Thrilling his former co-star and an ecstatic audience, he sang ‘Edelweiss’ to her.

Decades later, Andrews did not mince words about Plummer’s on-set behaviour in one of their final interviews together during The Sound of Music 50th Anniversary in 2015. Asked whether he had been a “curmudgeon” on set, she said: “Afraid so. But a delicious one. But I’m used to that because (he husband) Blake (Edwards) was one also.”

Plummer, in turn, praised Andrews for her leadership, stating, “We followed her like Saint Joan into battle. You would have agreed with me had you been there.”

Acknowledging her importance, he told her, “It was your film and you drove it… I didn’t want to have anything to do with it.”

Andrews, reflecting on Plummer’s initial reluctance, replied, “Not then, but you are glad now, I think.”

All Sound of Music fans will be relieved to know that he smiled and affirmed, “Yes, I am. I sure am.”

The Sound of Music is on BBC2 at 3.50pm on Sunday