HE was fascinated by the tangled sex lives of his patients, but Sigmund Freud has always had a reputation for rigid morality when it came to his own marriage.

Now a thick, leather-bound guest book found in a hotel in Maloja, in the Swiss Alps, after more than than 100 years has suggested that the father of psychoanalysis may have been quietly indulging in a ménage à trois with his wife and her sister.

The register was found by Franz Maciejewski, a German writer researching a book on Freud. In an entry for August 13, 1898, the occupants of one double room at the Hotel Schweizerhaus signed in as “Dr Sigm Freud u Frau”, German for “Dr Sigmund Freud and Wife”.

“I knew what date to look under because Freud wrote about his holiday to his wife Martha, and I just ran my finger down the page. And there was his familiar writing,” said Maciejewski. “But I was astonished to see that he had registered Minna (Martha’s sister) as his wife.”

There has been other circumstantial evidence of Freud’s extramarital relationship but Maciejewski said: “This is the smoking gun — hard proof of their affair.”

Freud — whose British descendants include Lucian Freud, the artist, Sir Clement Freud, the broadcaster, and Bella Freud, the fashion designer — has previously been seen as a faithful and not particularly passionate husband. He once said half-jokingly that he could have benefited from more experience of women in his youth.

Experts believe this view may have to be revised on the basis of the guest book discovery.

Peter Gay, a Freud biographer who has long argued against the idea that Freud and Minna had an affair, said: “It (the guest book entry) makes it very possible that they slept together.”

Freud first came into contact with Minna when he was wooing Martha Bernays, his future wife. The couple married in 1886 and had six children. According to one biographer, their only conflict in more than 50 years of marriage was about whether mushrooms should be cooked with their stalks on or off.

In 1896 Minna moved in and the gossip began. She became a permanent fixture, even moving to London with them. The Freuds moved from Vienna to Britain to escape the Holocaust before Sigmund’s death from cancer in 1939.

Minna enjoyed discussing with Freud his work on the sexual motivations of his patients; Martha called this part of her husband’s work “pornography”.

Peter Swales, a British historian, has argued that Minna became pregnant by Freud in 1900 and had an abortion. The trip to Switzerland came two years after Minna moved in. The couple stayed for three days.

In a postcard to his wife dated August 13, the day of his arrival in Maloja, Freud enthuses about the beauty of the glaciers.

Carl Gustav Jung, the Swiss psychoanalyst, said that in 1907 Minna confessed to him that she felt guilty about her relationship with Freud. “I learnt that Freud was in love with her and that their relationship was indeed very intimate,” Jung reported.

Many scholars dismissed this as a slur by Jung on his rival. The late Kurt Eissler, former director of the Sigmund Freud Archives in Vienna, wrote in 1993: “In one respect Freud was undeniably superior to Jung: his sexual record was lily-white.”

Freud was as open about his patients’ sex lives as he was tight-lipped about his own.

Swales hailed the find as “the icing on the cake” in opening up Freud’s own secrets.

“They were playing out an imposture,” he said. “This discovery makes Freud much more interesting as a human being but more dubious as a sexual scientist because he was less than honest about his own sexuality.”

At the Hotel Schweizerhaus, Jürg and Karoline Wintsch, the owners, are toying with calling the room where the couple stayed “The Freud Room”.

Talented clan

Since his arrival in London in the 1930s, the descendants of Sigmund Freud have spread their tentacles across the British cultural and political landscape.

Sigmund’s grandsons include Lucian Freud, who is regarded as the nation’s greatest living artist, and Sir Clement Freud, the writer and former Liberal MP.

Other members of the famous clan include Lucian’s daughters, Bella Freud, the fashion designer, and Esther Freud, the author whose debut novel Hideous Kinky was turned into a film starring Kate Winslet.

Clement’s offspring include Emma Freud, the television presenter married to Richard Curtis, the film writer behind hits such as Four Weddings and a Funeral. Talented clan

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