Dr Alex Comfort had a conventional family life with his wife Ruth, and their son Nicholas for many years after the couple met at Cambridge University (Family pictured in 1966).
The book, published in 1972, featured detailed illustrations of sex positions he used to experiment with Jane (a Plan B, after Comfort initially took Polaroids of himself having sex with Jane to horrified publishers).
The gerontologist met his wife Ruth at Cambridge University; before engaging in an affair with her university friend Jane decades later - inspiring him to write the book.
Comfort and Ruth's son Nicholas, who now lives a quiet life in south east London with his third wife, opened up about how his father's extramarital affair had played out before he wrote The Joy of Sex.
Bearded Charles, one of the artists on the book (he usually painted flowers), and German-born Edeltraud, volunteered to recreate Comfort and Henderson's sex life 'and she got him through the positions with Teutonic efficiency', said Nick.
