Why I nixed sex with ‘less than chivalrous’ JFK Jr.

Brooke Shields said John F. Kennedy Jr. was “less than chivalrous” after she refused to have sex with him on their first and only date.

The “Blue Lagoon” beauty, 57, recalled details of her romantic encounter with the late heartthrob during an interview with Howard Stern Tuesday, adding that Kennedy kept saying she looked like his famous mom, Jackie Onassis.

“I was so madly in love with him since the time I was 3,” Shields said of Kennedy. “My mom would say, ‘That’s the boy you’re going to marry.’ “

The model and actress — who is back in the spotlight following the release of her Hulu documentary “Pretty Baby: Brooke Shields” — told Stern that she crossed paths with Kennedy while she was in Aspen, Colorado, for a wedding in the 1980s.

Kennedy — who was five years older than Shields — was in town on a family ski trip and invited the star on an outing on the slopes.

“I had never skied before in my life,” Shields spilled, saying she tried hard to impress the hunky political scion before embarrassing herself.

“I had to get ski lifted out because I went into the trees and couldn’t get off the mountain,” she stated.

The “Endless Love” actress revealed that Kennedy “didn’t help her” on the slopes, but she later joined him at a rowdy bar for drinks with some of his family members.

Afterward, the son of President Kennedy and Onassis asked Shields if she wanted to go back to his ski chalet.

“He was like, ‘Do you want to get out of here?’ And I was like, ‘Uh, yeah, I do want to get out of here, John Kennedy,’ ” the star recalled.

However, the date delved into strange territory, according to the actress.

“He kept saying I looked like his mother,” she said. ‘Which was really interesting, it was a compliment, but also like ‘I don’t know how to feel about this?’ “

Kennedy and Shields soon shared a smooch, which the “Suddenly Susan” star described as “the best kiss I have ever had in my life.”

“It was beyond not disappointing,” the beauty cooed. “The lips are beautiful, and the face is amazing, and the body and the person … and he was down to earth.”

However, despite the lusty lip-lock, the starlet turned down sex with Kennedy, saying: “I was like, ‘Oh my God, you’re falling in love and if you sleep with him, he may not talk to you again and you can’t handle that.’

“I wasn’t playing a game,” she continued. “I really was just so afraid of being really hurt because if I slept with him I would have given him my entire universe, my heart, my everything.”

After refusing Kennedy’s advances, Shields was forced to call a cab back to her own lodgings in Aspen — describing her date as “less than chivalrous” because he left her to her own devices.

She told Stern that she realized that she made the right decision as she was ignored by Kennedy on the ski slopes the following day.

“He didn’t look at me and he didn’t talk to me,” Shields said. “On the one hand, I was like ‘S–t.’ On the other hand, I was like, ‘Oh, thank God, because he still might not have talked to you.’

“He showed his true colors in that,” she defiantly declared.

Kennedy went on to marry publicist Carolyn Bessette in 1996. The couple tragically died in a plane crash three years later.

Shields, meanwhile, had a short-lived marriage to tennis ace Andre Agassi. She has been married to her second husband, Chris Henchy, since 2001.