JFK Jr once had a playdate with ‘Preppy Killer’ Robert Chambers… and it didn’t go well

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John F Kennedy Jr once had a childhood playdate with the boy who would later become the 'Preppy Killer', Robert Chambers, a new book has revealed. 

The former President's son went to dinner with him and they watched a show together, but Jackie Kennedy's assistant and nanny Kathy McKeon has said the evening did not go as planned.

In her book, she told how Chambers' mother kicked her son under the table for apparently saying the wrong thing. 

John F Kennedy Jr attending the funeral of a former aide and family friend David Powers a year before he died

Robert Chambers is taken into court by police detectives in New York. Chambers, the so-called Preppy Killer who served 15 years in prison for strangling an 18-year-old woman in New York's Central Park, was arrested in Manhattan on drug charges after a violent struggle with police

Robert Chambers pictured being taken to court in 2007 when years earlier he had a play date with JFK Jr

McKeon used to babysit JFK Jr between 1964 and 1977, and on one occasion decided to take him out to cheer him up after a bout of bronchitis. 

Chambers' mother was a nurse who had helped care for him during his illness. 

After the outing, McKeon recalled how it was unfortunate that the nurse's son was a few years younger than JKF Jr, who would later die along with his wife Carolyn Bessette-Kennedy and her elder sister Lauren after the small plane he was flying crashed in 1999.

Kathy McKeon was a 19-year-old fresh off the boat from Ireland when she was hired to be Kennedy's live-in assistant in 1964. The two are pictured above at McKeon's wedding

The former nanny told People Magazine: 'He kept saying the wrong thing at the restaurant, and his mother would get mad at him.

'Every time Robert would say the wrong word, she’d give him a kick under the table.

'She was trying to make him sound all grown-up so he was more in John’s range … But he wasn’t. This kid was only four or five. [While John was seven or eight]'

The nurse called to try and arrange a second date, but she politely but firmly declined the invite.

She was reminded of the play date years later when a 19-year-old Chambers was charged with killing a teenager in Central Park in what he claimed was rough sex that got out of hand. 

Also in the book, Jackie Kennedy's longtime live-in assistant has revealed the former first lady's extremely restricted diet. 

Kathy McKeon was hired to work for Jackie in 1964, when she moved to New York City after the assassination of her husband.

In the book, Jackie's Girl, the now 72-year-old Irish immigrant, details her 13 years living at the Kennedy apartment - including candid details about the stick-thin socialite's eating habits.  

Jackie Kennedy's former live-in assistant has detailed the former first lady's (pictured in 1977) very restricted diet  

McKeon says she once complained about gaining weight after moving to America and Jackie offered to help her lose some weight. 

Jackie got together with her personal cook and devised a diet for McKeon that she says was 'almost exactly' the same as what 'Madame' (Jackie's name to the staff) ate every day.

'The two of them mapped out a regimen: a boiled egg and tea in the morning, cottage cheese with fresh fruit for lunch, and a poached chicken breast or fish with a salad or steamed vegetables for dinner. Plain yogurt when I wanted a snack,' McKeon recalled in an excerpt published in People.

DailyMail.com estimates that the diet was only about 600 calories a day - far less than the 2,018 calories a day a 120-pound, moderately active woman like Jackie would have needed. 

But that doesn't mean that was all she was eating.

McKeon remembers often running into Jackie in the kitchen late at night.

'Sometimes we’d crash into each other at night in the kitchen pantry. She didn’t put on the light because she didn’t want anyone to know she was in there!' McKeon said. 

One time, she found the former first lady eating ice cream straight from the tub. 

'She was eating ice cream out of the container with a big spoon,' McKeon said. 'Not a teaspoon but a big spoon! She was a lot of fun.'

And Jackie always made sure to eat while drinking.  

While being courted by Greek shipping magnate Aristotle Onassis, who would later become her second husband, McKeon says Jackie would often heat up Jiffy pop on the stove for cocktail hour. 

Previous profiles of the first lady have detailed her obsession with her weight. 

Tish Baldride, Jackie's former social secretary, told Vanity Fair in 2004 that Kennedy was disciplined about maintaining her weight of 120 pounds and watched the scale 'with the rigor of a diamond merchant counting his carats'.

And it appears that that obsession extended to others, according to McKeon. 

'She wanted to be sure Caroline didn't eat fattening stuff and always dressed nice,' McKeon said. 

In another incident, detailed by C. David Heymann in his book 'American Legacy: The Story of John & Caroline Kennedy', Jackie once reprimanded her daughter in public for wanting to order desert.

'You're much too fat. Nobody will ever want to marry you,' Jackie reportedly told her daughter.

Caroline was eventually given a serving of cherry Jello-O - without whipped cream - when her stepdaughter Christina Onassis stepped in. 

Heymann also says that Caroline's credit card was taken away once when her mother noticed a charge for two pounds of barbecued spareribs on the account. 

'After lecturing her daughter on the perils of excessive poundage, she canceled the credit card, but reactivated it when Caroline agreed to join her mother on jogs around the Central Park Reservoir.' 

John F. Kennedy tucks into a fruit cup while wife Jackie looks on at their wedding in 1953

John Loring, who worked with Jackie when she was an editor at Doubleday, told Harper's Bazaar in 2010 that the two would sometimes work through lunch and Jackie never seemed in a rush to order food. 

When anyone complained of hunger, Loring says Jackie would pull a bag of carrot sticks out of her purse and say 'Here, one of these will do the trick.' 

When Jackie became sick with cancer in the last year of her life, Loring says he knew something was wrong when he witnessed her eat dessert during a lunch meeting at famed New York City restaurant Le Cirque.

'After lunch, the waiter brought a variety of desserts. I'd never seen Jackie eat a dessert and suggested he take them away. "If you touch a single one of them, I'm going to stab you with my fork!" she warned. She ate all six desserts. 

'I knew that she knew there was no more need for carrot sticks. We didn't let it show, but we both knew. We walked over to Madison Avenue. I gave her a kiss on the cheek, and we went our separate ways,' Loring recalled