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This rare photo of Robert F. Kennedy (left), Marilyn Monroe and John F. Kennedy was taken during a party at the home of movie executive Arthur Krim on May 19, 1962 -- right after Monroe sang her famous, sultry rendition of "Happy Birthday" to President Kennedy during his 45th birthday celebration at Madison Square Garden.
Monroe was rumored to have had affairs with both brothers.
White House photographer Cecil Stoughton, who took the photo, kept it a secret for decades before releasing it in 2010. It is reportedly the only known photo of either Kennedy with Monroe.
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Frank Sinatra brought a lot to the table in his friendship with John F. Kennedy. It was the famous singer who introduced JFK to Marilyn Monroe, among other celebrities, after the then-presidential candidate attended a show at the Sands casino in Las Vegas while on a campaign break in 1960.
Sinatra also campaigned for Kennedy and organized his star-studded "pre-inaugural gala" that featured performances from Sinatra himself, Ella Fitzgerald, Gene Kelly and Nat King Cole.
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Even Barbra Streisand got starstruck at the sight of JFK. The president signed an autograph for the singer and actress when they met after the 1963 White House Correspondents Dinner.
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President John F. Kennedy met with stars Judy Garland, Carol Burnett and Danny Kaye in the Oval Office in November 1962.
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John F. Kennedy and Judy Garland struck up a friendship after first meeting when JFK was a junior senator from Massachusetts.
As president, he would sometimes call the Wizard of Oz star for an impromptu rendition of “Over the Rainbow," according to a recent memoir by Garland’s third husband, Sid Luft.
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(From left to right: Jackie Kennedy, Prince Rainier and Princess Grace of Monaco, and President John F. Kennedy)
The Kennedys hosted Prince Rainier and Princess Grace Kelly at the White House for a luncheon in their honor in 1961.
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John F. Kennedy Jr. dated actress Daryl Hannah on and off and on from 1989 to 1994 before he went on to date – and later marry in 1996 – Calvin Klein publicist Carolyn Bessette.
The former couple are pictured here watching a game between the New York Knicks and the Houston Rockets at Madison Square Garden in 1994.
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JFK Jr. also briefly dated Sarah Jessica Parker in 1991 after the two met while she was performing Off-Broadway.
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Arnold Schwarzenegger married into America's most famous political family in 1986 when he wed Maria Shriver, the daughter of JFK's sister Eunice Kennedy Shriver.
The two split in 2011after it was revealed that Schwarzenegger had fathered a child with former housekeeper Mildred Baena.
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Curb Your Enthusiasm star Cheryl Hines married activist Robert F. Kennedy, Jr. in 2014.
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Singer Taylor Swift and Robert F. Kennedy's grandson Conor Kennedy had a whirlwind summer romance in 2012 before parting ways.
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In August 2012, Taylor Swift was by Conor Kennedy's side during a visit the gravesite of his mother, Mary Kennedy, in Cape Cod, Massachusetts. Mary Kennedy, the estranged wife of Robert F. Kennedy Jr., committed suicide in May 2012.