The star told her closest friend of her isolation in a series of notes that are now up for auction

Greta Garbo, the elusive Hollywood actress of the 1930s, was so inscrutable she was known as the Swedish Sphinx.

Born in Stockholm, she is best remembered for leading roles in the movie classics Queen Christina and Anna Karenina and for the famous phrase “I want to be alone” – a line her character speaks in her 1932 hit Grand Hotel. It fitted her image as a star who shunned the glitz and hoopla of Hollywood.

Now a cache of 65 intimate letters, to be sold at auction, show just how lonely Garbo’s hours of solitude really were. The pencilled sheets were all written to her great friend, the Austrian actress and writer Salka Viertel, over a period of 40 years between 1932 and 1973. The candid evidence of Garbo’s introspection is expected to fetch as much as $60,000, such is the interest of film collectors.

In one letter, penned to Viertel in 1937 during a trip to Sweden, Garbo claims: “I go nowhere, see no one.” She adds that she did the same when in Hollywood, and pleads with her old friend to rescue her. “It is hard and sad to be alone, but sometimes it’s even more difficult to be with someone … When we are here on Earth it would be so much more kind if for this short time we would be forever strong and young. I wonder why God preferred it this way … somewhere in this world are a few beings who do not have it as we have, of that I am certain. And if I would stop making film I could go and see if I could find out a little about it.”

The letters first came up for sale in 1993,when they were bought by a fan from Florida. They are now being auctioned by a private owner and their contents will add weight to the Garbo myth, confirming her as the original model of a Nordic Noir heroine.

Although Garbo’s onscreen air of melancholy was clearly genuine, she found the popular idea that she always avoided company irritating. “I never said: ‘I want to be alone,’” she once explained in a 1955 Life magazine article. “I only said, ‘I want to be let alone! There is all the difference.”

Facebook Twitter Pinterest One of the Garbo letters on sale at Swann Auction Galleries. Photograph: Swann Auction Galleries

Another bundle of letters, sold by Sotheby’s two years ago, was sent to another of her female confidantes, the Swedish countess, Marta Wachtmeister, and expressed similar feelings of isolation. Living in Hollywood, far from the northern climate of her homeland, it is clear that the actress relied on her friends in Europe to help her cope with the exasperations of the film industry.

Viertel, regarded by biographers as her closest friend, co-wrote a number of Garbo’s greatest films and appeared opposite her in the German-language version of Anna Christie, filmed in 1930. In later life she moved to Switzerland to be near her son, the writer Peter Viertel, married to the Scottish film star Deborah Kerr. Right up until Viertel’s death in 1978, Garbo (“Miss G” or “Grusha”) would leave her home in New York to join her friend.

The letters to Viertel, to be sold in the fine books and manuscripts sale at Swann Auction Galleries, also contain several insights into Garbo’s dismissive views on directors and producers. In a letter from around 1935 she discusses the run-up to shooting her 1936 film Camille with producer Irving Thalberg and says that she would rather switch studios and work with David O Selznick, who went on to make Gone with the Wind three years later.

“God help me if Thalberg does it alone … I could write Mayer otherwise and perhaps he could let Selznick do Camille. We would have to move over to United [Artists].”

Later she writes: “Please ask Thalberg to think very carefully about Camille. It’s so like Anna Karenina that I am afraid. It’s devastating to do the same story again.”

• This story was corrected on 7 October 2019. Irving Thalberg was producer of Camille, not director as originally stated; the director was George Cukor. In Grand Hotel, Garbo’s character does say the line “I want to be alone”.