AS A CLOSE PERSONAL FRIEND TO PRINCE Charles, Camilla Parker Bowles occupies a position as old and respected in its way as the monarchy itself. According to Lady Colin Campbell, author of Diana in Private, the institution of ''confidante'' is the source of a tremendous amount of kudos and social influence. And although Parker Bowles's relationship with the Prince is currently raising eyebrows in England, earlier kings conducted far more notorious liaisons. Charles II (reign 1660-85), for example, had no legal heirs by his wife, Catherine of Braganza, but fathered some 14 illegitimate children by seven of his countless mistresses. One of his liaisons, the actress Nell Gwyn, bore Charles two sons, the first of whom she threatened to throw from a high window because he had been given no royal title. Charles allegedly resolved the crisis by calling out, ''Nell, don't kill the Duke of St. Albans!''

Mistresses, as a rule, did get their way. Kings bestowed titles on them and their offspring, many of whom occupy the ranks of British aristocracy today: Five branches of Princess Diana's own family, the Spencers, trace their lineage directly to Charles II's illegitimate children. The first Earl Spencer's daughter, Georgiana, later Duchess of Devonshire, was one of the many interests of the future George IV (reign 1820-30).

Camilla Parker Bowles herself can point to a confidante ancestor. Her great- grandmother Alice Keppel was the last love of Queen Victoria's eldest son, Bertie. The 56-year-old Prince of Wales had bedded actresses Sarah Bernhardt and Lillie Langtry when he met Alice, the 29-year-old wife of George Keppel, an army officer. Even after the Prince became King Edward VII, he vacationed on the Continent with his mistress in a relationship that was so openly acknowledged that Queen Alexandra invited her to the King's bedside when he was dying in 1910. Of all the royal confidantes, Alice Keppel may have described the role most deftly. ''A royal mistress,'' she is reported to have said, ''should curtsy first, then leap into bed.''