Rosemary Kennedy died on 7 January of natural causes at the age of 86 in a hospital in Fort Atkinson, Wisconsin, a town far from any large American city. She had spent nearly all of her adult life in a facility for the disabled in the nearby community of Jefferson.

Rosemary Kennedy died on 7 January of natural causes at the age of 86 in a hospital in Fort Atkinson, Wisconsin, a town far from any large American city. She had spent nearly all of her adult life in a facility for the disabled in the nearby community of Jefferson.

At her bedside were her four surviving siblings: Edward, Eunice, Patricia, and Jean, all members of what many refer to as America's royal family. They and their deceased brothers and sister, Joe Jnr, John, Robert and Kathleen, all conducted their lives in the limelight.

Download the new Independent Premium app Sharing the full story, not just the headlines

Not Rosemary. As a young woman, the eldest sister of the clan was presented to the Queen and was presumed to lead a charmed life. In fact, as she grew older, Rosemary's parents became increasingly embarrassed by her erratic behaviour.

In 1941, her father (without telling his wife) took the extreme step of having her lobotomised, an experimental procedure administered by the fashionable but controversial Walter Freeman, one of the most colourful doctors ever to wield an ice-pick. The operation went horribly wrong and Rosemary spent the rest of her life in an institution.

Her passing has reopened one of the darkest - and least known - chapters in the dynasty's tragic history.

For decades, Kennedy family biographers have debated the puzzling course of Rosemary's life. Some believe, as the family has long maintained, that she suffered from mental retardation and underwent the lobotomy - a now-obsolete brain operation intended to treat psychiatric disorders - because of emotional instability.

Others, however, have questioned whether Rosemary had a serious mental disability at all. Arriving at the truth, however, is not easy. Few records are available that shed light on Rosemary's life and the Kennedy family has spun varied stories about her childhood, adulthood, and mental health.

Critics of the Kennedy family's version of events point out that as a young adult Rosemary kept a coherent diary, sometimes travelled unescorted, served as a hostess at family parties, visited the White House and had an audience with King George VI and Queen Elizabeth. In 1939 she attended the coronation of Pope Pius XII with her family in Rome.

"Before her lobotomy, she seemed healthy and attractive," says Harvey Rachlin, author of The Kennedys: A Chronological History 1823-Present. "She was never an obstacle, embarrassment, or anything very negative. It has always been my feeling that her mental condition was borderline, and that the lobotomy that her father Joe authorised really messed her up."

Daily coronavirus briefing No hype, just the advice and analysis you need Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive morning headlines Monday - Friday plus breaking news alerts by email Update newsletter preferences

Her lobotomy, it is often maintained, resulted from her parents' inflexible expectations of proper behaviour for a Kennedy child. "Joe had two principal concerns about Rosemary," Barbara Gibson and Ted Schwarz wrote in their book about the family's matriarch, Rose Kennedy and Her Family: The Best and Worst of Their Lives and Times. "She was not the competition-oriented ideal of Kennedy womanhood, and he thought her sexuality was too intense and untempered by the moral strictures to which the other daughters had adhered. Joe destroyed a portion of her brain rather than risk what she might become if allowed to follow her own path in life."

Rosemary was born on September 13, 1918, in Boston. According to Gibson, who worked as personal secretary to the girls' mother, Rose Kennedy, the birth was difficult. Rose often related how attending nurses tried to halt the progress of labour until the doctor arrived, a process that may have injured the baby .

Some published accounts have described Rosemary as an unathletic child who reached developmental milestones later than others; who had trouble learning to read and write and whose easygoing personality sharply contrasted with the driving vivacity of her siblings. The family's rapid-fire banter around the dinner table baffled her. Instead she was placid and friendly - and her beauty often required her older brothers to fend off suitors. But placid and easygoing were not virtues highly valued in the Kennedy family. Rosemary "would never be a typical Kennedy woman," Gibson and Schwarz wrote.

"I am not convinced that she was mentally disabled," says Gerald O'Brien, a professor of Social Work at Southern Illinois University Edwardsville who has researched Rosemary's life and studied her role in the family. "Back then, mental retardation was not a clear category and it wasn't gauged in any accurate way."

Yet for decades, even in a statement to the press upon her death, the Kennedys have cited Rosemary's mental retardation as her defining disability. And they have referred to her intellectual deficits as the inspiration for her sister Eunice's founding of the Special Olympics and the family's generous support of other charitable causes benefiting the retarded.

By some accounts, her behaviour grew increasingly volatile after 1939. There are stories of her smashing objects and even kicking her grandfather. Outbursts of anger and bouts of depression may well have been her response to feelings of not belonging in her family and her parents' dissatisfaction with her. Her father, who had risen to the lofty heights of US Ambassador to Britain, could only see this behaviour as a threat to his position and ambitions for the family.

By 1941, Rosemary was living in a convent school in Washington, D.C., where her late night rambles caused concern. "The nuns feared that she was picking up men and might become pregnant or diseased," observed Kennedy family chronicler Laurence Leamer. A Kennedy in either condition would be disastrous.

"Joe liked to cut away at a problem and then move on," wrote Leamer, possibly explaining why lobotomy seemed a potential solution to the quandary Rosemary presented.

Then a new procedure, lobotomy involved the severing of neural connections between the frontal lobes of the brain and the thalamus (contrary to popular belief, most lobotomy patients did not have parts of their brains removed). The aim was to dull the intensity of the patient's overactive emotional impulses, thought to be the cause of many mental diseases. Lobotomists hoped to replace patients' suicidal feelings, deep depression and obsessive behaviours with the emotional detachment, lack of foresight and other more manageable consequences of severed frontal lobes.

This form of surgery grew popular in the United States and Europe between the late 1930s and the mid 1950s, a time when psychiatric medicine offered patients few treatments other than psychotherapy - largely ineffective for patients with serious psychoses - and electric shock therapy, insulin coma, or chemically induced convulsions. Many patients faced decades of confinement in abysmally run mental hospitals - and by comparison lobotomy appeared a promising solution to mental problems. About 50,000 Americans underwent lobotomy between 1936 and the 1970s.

Joe Kennedy first took Rosemary to a Boston physician, who refused to recommend lobotomy. Next he conveyed her to neurologist Walter Freeman, America's strongest promoter of psychiatric surgery. The grandson of the first brain surgeon in the United States and a highly respected practitioner of his medical specialty, Freeman was appalled by the waste of human potential he saw in the mentally ill and the desperation he found among patients and their doctors.

Freeman often employed unorthodox methods: at various times he applied a carpenter's mallet and an ice pick in his operations - and he once lobotomised a recalcitrant patient in a motel room. He did not, however, advocate lobotomy for mental retardation, he performed it for debilitating tension and anxiety.

Whether Freeman observed strong emotional tension in Rosemary - or her persuasive father convinced the doctor that the tension was present - Freeman agreed that lobotomy was worth a try (his papers are silent on the question of Rosemary's treatment, and we may never really know why he and his neurosurgeon partner James Watts considered her a suitable patient).

Joe Kennedy approved the surgery without the knowledge of his wife, who was travelling abroad.

The lobotomy, an indisputable disaster, left the 23-year-old Rosemary inert and unable to speak more than a few words. Freeman had cut too deeply. She eventually regained the ability to walk but permanently lost the initiative and mental capabilities she needed to live with even partial independence.

If Rosemary was a poor fit within the Kennedy family before the operation, she emerged from surgery a woman lacking any status as a member of her clan. She was a shame, a blight on the family. In 1949 she was sent to live at St. Coletta's School for Exceptional Children in Wisconsin. Rose Kennedy did not see her daughter for twenty years, and no family member seems to have visited her there until 1958, when John F Kennedy secretly paid a call while campaigning in Wisconsin. Meanwhile, the family publicly attributed her disappearance from view to her reclusiveness, and at one point it even circulated a story that Rosemary was busily engaged as a teacher of the disabled.

Not until John Kennedy became President in 1961 did the family acknowledge that Rosemary was disabled; her problem was mental retardation, not lobotomy. After Joe Kennedy's death a few years later, she gradually resumed a role in the family. She received visits from her mother and sisters and enjoyed travelling with an escorting nun to her childhood home at Cape Cod. Her speech was impaired, her arm palsied, and her walk limping.

There were two sides to this tragedy. First and foremost, Rosemary was deprived of her life's promise. But her treatment and the family's long denial of her condition harmed all of the Kennedys. Laurence Leamer called her lobotomy "the emotional divide in the history of the Kennedy family, an event of transcendent psychological importance ... Unlike all of the subsequent deaths and accidents, no mark of patriotism, heroism, daring or even dread circumstance could be attached to this act."

One lesson we can learn from Rosemary Kennedy's life has nothing to do with a young woman's psychiatric problems or a father's misplaced faith in the curative powers of a new medical treatment. It is that the healthiest families guide children toward happiness and independence by appreciating and cultivating the qualities they possess. Rosemary was born into a family that wished her to be something different, and for that she suffered.

Jack El-Hai is the author of 'The Lobotomist: A Maverick Medical Genius and His Tragic Quest to Rid the World of Mental Illness', a biography of Walter Freeman published this month by John Wiley & Sons.