Neil Diamond performs on the 2005 "Today" Show Summer Concert Series on May 6, 2005.
James Devaney/WireImage.com

The secret is out: "Sweet Caroline," Neil Diamond's classic hit, is about President Kennedy's daughter.

"I've never discussed it with anybody before — intentionally," the singer-songwriter, 66, told The Associated Press Monday.

He told her he wrote the song for her after recently performing it via satellite at her 50th birthday party.

Diamond said he was "a young, broke songwriter" when he came across a photo of Kennedy as a girl "dressed to the nines in her riding gear, next to her pony" in a news magazine, he told the AP.

"It was such an innocent, wonderful picture, I immediately felt there was a song in there," he said.

So he penned the tune, years later in a Memphis, Tennessee, hotel room, in less than an hour.

"It was a No. 1 record and probably is the biggest, most important song of my career," he said, "and I have to thank her for the inspiration."

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