The Heartbreaking Moment Jackie Kennedy's Assistant Comforted Caroline and John After Their Uncle RFK's Assassination

As Jacqueline Kennedy Onassis‘ live-in assistant and sometime nanny between 1964 and 1977, Kathy McKeon was there for some of the biggest — and most heartbreaking — moments in Caroline and John Jr.’s young lives. Among them was the assassination of their uncle Robert F. Kennedy in June 1968 — just five years after their father, John F. Kennedy, was shot and killed.

McKeon, now a 72-year-old grandmother of six, reveals new details about how the tragedy unfolded in her upcoming memoir, Jackie’s Girl, due out May 9 and excerpted in this week’s issue of PEOPLE.

In Jackie’s Girl, McKeon recalls how the former first lady asked her to comfort Caroline, then 10, and John, then 7, after their Uncle Bobby’s death:

“Will you talk to John and Caroline?” she asked, her voice a torn whisper. “Their uncle passed away.”

“I’m so sorry Madam,” I murmured.

“I know,” she said bitterly. “Same story all over again.”

I found John and Caroline crying in John’s room.

“Your Uncle Bobby is up in heaven,” I tried to console them. “Let’s choose a dress for you to wear,” I suggested gently to Caroline.

She knew without asking that I meant for the funeral.

Michael Ochs Archives/Getty Images

McKeon tells PEOPLE now, “It was a very sad day, it was a sad day for everybody.”

The former first lady and her children were very close to JFK’s brother, the junior senator from New York, who spent many happy hours playing with John and Caroline and giving them piggyback rides in their home at 1040 Fifth Avenue in New York City.

STORY BEHIND THE STORY: Story Behind the Story: Jackie Kennedy and JFK’s Legacy

The children “were very upset that Uncle Bobby was gone,” McKeon recalls. “He was very, very good to them.”

McKeon, who rode the funeral train to Washington, D.C., with the family, recalls the mood on the trip as “very, very quiet and very, very sad.”

Jackie sat with RFK’s widow, Ethel Kennedy, on the train, which also carried in the back the senator’s casket, wrapped with the American flag.

“It was very, very sad and a very emotional trip down to Washington,” McKeon says, recalling how RFK’s children, cousins and other family members cried on and off throughout the journey.

For more from McKeon on Jackie’s life after JFK, check out this week’s issue.

Also on sale now: PEOPLE’s commemorative edition Jack & Jackie: Remembering Camelot.