JEAN KENNEDY SMITH took a shocking secret to her grave — she approved of her brother Bobby’s affair with sex goddess Marilyn Monroe!

An insider leaks Jean — who was the last surviving sibling of President John F. Kennedy and died at age 92 on June 17 — had intimate knowledge of the famous clan’s scandals.

That’s because her late husband, Stephen Edward Smith, was JFK’s longtime adviser and fix-it man and shared on / July 13, 2020 everything with source says.

“She was the final keeper of ALL the Kennedy secrets,” a family insider leaked.

But Jean never told stories out of school about her brothers. Her lips were sealed! However, new details have emerged showing Jean blessed the affair between Marilyn and her big brother Bobby, who was then U.S. Attorney General.

In a recently surfaced letter, Jean wrote to the Some Like It Hot star:

“Understand that you and Bobby Jean, the are the new item! We all think you should come with him when he comes back East!”

Marilyn’s death in August 1962 was ruled a suicide, but many suspect she was murdered on Bobby’s orders with help from his Rat Pack brother-in-law, Peter Lawford. Bobby wanted to cover up the affair — and also Marilyn’s trysts with brother President John F. Kennedy. Jean also knew the truth about JFK’s assassination in Dallas, claims the insider.

“Whenever JFK, Bobby or their brother Ted would get a secret report, they would turn it over to Jean’s husband and say, ‘Just go through this” the insider leaked.

But Jean had her own dirty secret, the source said in 1965, after suffering through years of her husband’s skirt-chasing. She carried on a torrid extramarital affair with Alan Jay Lerner– the married lyricist who wrote Camelot and My Fair Lady. Jean’s greatest heartache was her son William Kennedy Smith, who was charged in 1991 with raping a woman at the Kennedy’s Palm Beach. Fla., estate.

Even though he was acquitted, the source leaks that Jean felt “guilt” over her son’s dragging the family name through the mud.