Maria Riva, daughter of movie star Marlene Dietrich, first met Rosemary Kennedy in 1938 when the family was vacationing in France. She says she grew close to the Kennedys because of her mother's affair with Joe Kennedy Sr.
Riva, who's previously said she felt "gawky" around the athletic Kennedy children, says she might have latched on to Rosemary's different behavior. "Perhaps being two misfits, we felt comfortable in each other's company," Riva writes.
See photos of Rosemary Kennedy:
11th May 1938: Rose Kennedy (centre), wife of multi-millionaire and US ambassador to Britain Joseph Kennedy, and two of her daughters, Kathleen Kennedy (Marchioness of Hartington) and Rosemary Kennedy (right), leaving to be presented at Court. (Photo by Keystone/Getty Images)
UNITED STATES - DECEMBER 01: Washington, December 1937. On the left: Joseph Patrick KENNEDY, his daughters Jean (age 9), Eunice (age 16) and Patricia (age 13). Behind them is John Fitzgerald KENNEDY (future president of the United States). On the right: Rose Fitzgerald KENNEDY with her sons and daughters, Joseph KENNEDY JR. (age 22), Rosemary (age 19), Robert (age 12) leaning on the chimney, Kathleen (age 17) and Edward (age 6). (Photo by Keystone-France/Gamma-Keystone via Getty Images)
UNITED KINGDOM - JANUARY 01: Rosemary And Eunice Kennedy With Edward Moore On Arrival At Plymouth In 1938 (Photo by Keystone-France/Gamma-Keystone via Getty Images)
Rosemary, John, Eunice, Joseph Jr, and Kathleen Kennedy, Hyannisport, Massachusetts, Summer 1925. (Photo by PhotoQuest/Getty Images)
Seated at right, American socialite and philanthrophist Rose Kennedy (1890 - 1995) poses with her children, from left, Joseph P Kennedy Jr (1915 - 1944), John F Kennedy (1917 - 1963), Kathleen Kennedy (1920 - 1948), Rosemary Kennedy (1918 - 2005), and Eunice Kennedy, Brookline, Massachussetts, 1921. (Photo by Bachrach/Getty Images)
Arriving from Europe by clipper, Rosemary Kennedy (left), daughter of Joseph Kennedy, Ambassador to England, is greeted by sister Jean.
(Original Caption) Photo shows, left to right: The Missies, Eunice and Rosemary Kennedy, as they sailed yesterday on board the S.S. Manhattan of the United States Lines, bound for England, to join their family at the Ambassador's residence at Prince's Gate. Rosemary, has been a student at Marymount Convent, in Tarrytown, N.Y., while her sister Eunice, studied at the Sacred Convent in Noroton, Connecticut. (Photo by George Rinhart/Corbis via Getty Images)
(Original Caption) American Embassy 'at home'...Mr. Joseph Kennedy, the American Ambassador, and Mrs. Kennedy, entertained nearly 1,500 Americans at an Embassy party at the American Embassy in Prince's Gate, London, S.W., to celebrate Independence Day. Photo shows: Miss Rosemary Kennedy, left, chatting to friends at the garden party today. (Photo by George Rinhart/Corbis via Getty Images)
Rose Kennedy sits with three of her young children: Joseph, Jr., Rosemary, and Jack.
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Riva says she quickly bonded with Rosemary, who she describes as "the damaged child amidst these effervescent and quick-witted children." But Riva adds she grew distant from Rosemary after finding out about the relationship between their parents.
Rosemary's lobotomy wouldn't happen until years later, when her father decided the procedure could cure her behavioral problems. The operation would leave her institutionalized for the rest of her life.
Rosemary was one of the earliest lobotomy patients; the procedure was eventually performed 50,000 times in the U.S. The surgical procedure's poor success rate and devastating side effects led to it being scrapped in the 1950s.
RELATED: See photos from JFK and Jackie O's wedding:
John F Kennedy and Jackie O through the years
John F Kennedy and Jackie O through the years
Massachusetts, USA, 1950's, President of the United States of America John F, Kennedy pictured as a young man with his wife Jackie Kennedy (Jacqueline Bouvier) early in their marriage (Photo by Popperfoto/Getty Images)
Massachusetts, USA, 1950's, President of the United States of America John F, Kennedy pictured as a young man with his wife Jackie Kennedy at home (Photo by Popperfoto/Getty Images)
NEWPORT, RI - SEPTEMBER 12: John F. Kennedy and Jacqueline Kennedy outside St. Mary's Church after their wedding on September 12, 1953. (Photo by Charles F. McCormick/The Boston Globe via Getty Images)
UNSPECIFIED - CIRCA 1754: US President John Kennedy, President Charles de Gaulle and Jackie Kennedy in Paris at the Elysee Palace May 31, 1961 (Photo by Universal History Archive/Getty Images)
1956: Waiter clearing dishes fr. table in front of actor David Niven (3R) sitting next to Sen. Jack Kennedy's wife Jackie (2R) w. others dining at society gala sponsored by wife of US Amb. to Cuba, in the ballroom of the Waldorf Astoria Hotel. At the far left is Jackie's sister Caroline Lee Bouvier (later Canfield, Radziwill, and Ross). (Photo by Yale Joel/The LIFE Picture Collection/Getty Images)
March 25, 1958: Sen. Jack Kennedy cuddling his darling baby daughter Caroline who is smiling as her mom Jackie looks on in delight while relaxing on bed at home. (Photo by Ed Clark/The LIFE Picture Collection/Getty Images)
JULY 20: John F. Kennedy and Jacqueline Kennedy. (Photo by Charles McCormick/The Boston Globe via Getty Images)
Sen. Jack Kennedy slyly lending an ear to his wife Jackie's giddy whisper as they sit together at table during cocktail hour before dining at society gala sponsored by wife of US Amb. to Cuba, at the Waldorf Astoria Hotel. (Photo by Yale Joel/The LIFE Picture Collection/Getty Images)
American future First Lady Jacqueline Kennedy (1929 - 1994) and her daughter Caroline pause on the stairs of their vacation home and look back down, Hyannisport, Massachusetts, September 1960. Ms. Kenney wears a trenchcoat and a flower-print scarf over her hair while Caroline is dressed in a overalls. (Photo by Alfred Eisenstaedt/The LIFE Picture Collection/Getty Images)
Jackie Kennedy and friends, circa 1960s. (Photo by Fotosearch/Getty Images).
CIRCA 1960s: Former First Lady Jacqueline Kennedy enjoys herself at a picnic circa the 1960s. (Photo by Michael Ochs Archives/Getty Images)
DISTRICT OF COLUMBIA, UNITED STATES - 1961: President Kennedy (R) with First Lady Jackie (L) (in fur-trimmed suit designed by Oleg Cassini) at his inauguration. (Photo by Leonard McCombe/Life Magazine/The LIFE Picture Collection/Getty Images)
PARIS, FRANCE - UNSPECIFIED DATE: American president John and Jackie Kennedy at the American Embassy during 1961 in Paris, France. (Photo by S010/COLLECTION SALINGER/Gamma-Rapho via Getty Images)
The newly-elected President John Fitzgerald Kennedy with wife Jackie after giving the traditional acceptance speech. USA, November 1960 (Photo by Mondadori Portfolio via Getty Images)
Frank Sinatra escorting Jacqueline Kennedy to her box at a gala, held at the National Guard Armory in Washington DC, the night before the inauguration of President John F. Kennedy, 19th January 1961. The gala was staged by Sinatra to help pay off the campaign debts of Kennedy and the Democratic Party. (Photo by GAB Archive/Redferns)
Portrait of American First Lady Jacqueline Kennedy (1960 - 1999) in the Red Room of the White House, Washington DC, January 15, 1962. During the filming of a CBS News Special program called 'A Tour of the White House with Mrs. John F. Kennedy,' she stands in front of an Alfred Wordsworth Thompson painting of the Civil War battle at Balls Bluff, Virginia. (Photo by CBS Photo Archive/Getty Images)
The President and Mrs. Kennedy attend a White House Ceremony February 19, 1963. (Photo by National Archive/Newsmakers)
First Lady Jackie Kennedy speaks to a guest while attending a White House ceremony January 8, 1963 in Washington, DC. (Photo by National Archive/Newsmakers)
UNITED STATES : A contemporary report ran: ?Caroline, five, moves into the big time. Big day for a small girl. The day she moved from the junior to the senior class. The day she rode not her own pony, Macaroni, but mother?s horse, Rufus, with her mother. The girl is Caroline Kennedy, five-year-old daughter of America?s President John Kennedy and his wife Jacqueline.? President Kennedy was assassinated later that year, on November 22. (Photo by SSPL/Getty Images)
18th October 1968: Millionaire shipping magnate Aristotle Onassis (1906 - 1975) with his wife Jackie (Bouvier Kennedy, 1929 - 1994). (Photo by Central Press/Getty Images)
Jackie Kennedy Onassis, Caroline Kennedy (left), John F. Kennedy, Jr., and Lee Rodziwill (Photo by Ron Galella/WireImage)
Jackie Onassis, Anthony Radziwill, and Tina Radziwill (Photo by Ron Galella/WireImage)
Jackie Onassis during Jackie Kennedy and Family Shopping in Capri - August 24, 1970 in Capri, Italy. (Photo by Ron Galella/WireImage)
Jackie Kennedy Onassis in Capri, Italy. (Photo by Ron Galella/WireImage)
Jackie Onassis (Photo by Ron Galella/WireImage)
Jackie Onassis with son John Kennedy Jr during Jackie Onassis Sighting at the Philharmonic Hall - December 13, 1971 at The Philharmonic Hall in New York City, United States. (Photo by Tom Wargacki/WireImage)
Washington, D.C. May 14th 1976. Jackie Onassis and Alexandrje Orfila at The Kennedy Center (Photo by Tom Wargacki/WireImage)
Jackie Onassis and Alex Orfila during OAS Party following the Kennedy Center Gala at Kennedy Center in Washington D.C., United States. (Photo by Ron Galella/WireImage)
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The Kennedy family kept Rosemary shielded from public scrutiny after the procedure, but her experience inspired some members of the family to campaign for better treatment for the mentally disabled.
Rosemary's condition has been cited as part of the reason Eunice Kennedy Shriver founded the Special Olympics in 1968.