Jackie's Former Assistant: JFK JR Turned From Scrawny Kid To People's Sexiest Man Alive 

Long before he grew up to become a national heartthrob and PEOPLE’s 1988

Sexiest Man Alive, John F. Kennedy Jr. was a “scrawny kid” who shied away from “rough-and-tumble sports,” recalls Kathy McKeon, Jacqueline Kennedy Onassis‘ live-in assistant and sometime nanny between 1964 and 1977.

McKeon, now a 72-year-old grandmother of six, reflects on her time with one of America’s most famous families in a new interview with PEOPLE and in her upcoming memoir,

She recalls seeing a more grown-up John Jr. for the first time in three years, after he had just finished boarding school, and being shocked by how handsome he had become.

“He came out of nowhere!” McKeon says now of the late son of Jackie and former President John F. Kennedy.

Adds McKeon’s husband, Seamus McKeon, who also knew John Jr., “[I saw him after] he had just finished boarding school and I said, ‘What the hell happened to you?’ You just couldn’t believe it. He was like the statue of David. Just like that.”

“Boy, oh boy, were we shocked when we saw” the transformation, he recalls.

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

The McKeons remained friendly with John Jr. throughout his life, which was tragically cut short at 38 when he and his wife, Carolyn Bessette, and her sister, Lauren, were killed in a plane crash in 1999. A year before his death, the McKeons visited the young couple in Hyannis Port on Cape Cod to help John and Carolyn update the house.

When she first learned that the plane John had been piloting was missing, McKeon says, “I didn’t believe it. It took me a long time to believe it. I said, ‘He’ll show up.’ And that didn’t happen.”

After attending John’s funeral, a devastated McKeon reminisced over scrapbooks. She writes in

, “I pulled out the scrapbooks where I kept pictures and letters from my life with the Kennedys. There was John taking a ski lesson … My life felt full of tender little clues of that other life I once had.”

She says of John, “[People] loved him because he had a really nice personality and he was very kind to everybody and he talked to anybody and he was funny and in no way fancy at all. He always looked so handsome and he wasn’t even dressed [up].”

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

Also on sale now: PEOPLE’s commemorative edition

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