John F. Kennedy Jr.’s close confidants spilled secrets about his fling with Madonna after the pop star admitted that he was the best sex of her life.

A source close to JFK Jr. exclusively revealed to Page Six that his romp with Madonna was “a fun adventure for him.”

“He did say something to me…So I knew that it did occur,” the insider said of their hookup. “He had a really fun time and a really good time [with Madonna].”

The source added that Kennedy Jr. and the “Vogue” singer only hooked up once, but they remained friends after.

JFK Jr.’s longtime chief of staff, RoseMarie Terenzio, agreed that they were able to maintain a flirty friendship after their “whirlwind” romance.

“We didn’t talk about his intimate life,” the “JFK Jr.: An Intimate Oral Biography” co-author exclusively told Page Six Friday.

“I just remember him saying that it was like a whirlwind little romance, but it didn’t really go further,” she said, noting, “And I know that there were a lot of scheduling issues involved because she was on tour.”

Terenzio — who also wrote “Fairy Tale Interrupted: A Memoir of Life, Love, and Loss” — explained that Madonna and Kennedy Jr. “friend-zoned each other” after their steamy rendezvous.

“They both just kind of moved on,” she said.

While they didn’t continue their physical relationship, Madonna and JFK Jr. moved forward with some cheeky flirting.

“They had a really cute banter and a nice friendship,” Terenzio said. “They didn’t see each other all the time or anything like that. But they had a cute, funny friendship.”

“That was their relationship. Like her giving him s–t and him giving her s–t,” she continued. “It was funny. At that time, two of the most famous people in the world, just like ripping each other and giving each other s–t.”

Terenzio said that Kennedy Jr. and Madonna would fax each other playful messages.

“That’s how they communicated,” Terenzio said.

Kennedy Jr. and Madonna ran in the same circles, so it was easy for them to stay connected.

“They worked out with the same trainer, so they saw each other sometimes,” Terenzio said, confirming, “They stayed friends.”

Earlier this week, Page Six exclusively revealed that Madonna dubbed Kennedy Jr. the best she’s ever had — with a caveat.

The “Like a Prayer” artist, 67, linked up with Grindr while promoting her new album, “Confessions II,” and answered some questions, including, “Who was your best d–k down?”

“I’m only going to name dead people,” Madonna said, before whispering, “John Kennedy Jr.”

Despite Madonna’s undeniable connection with Kennedy, the son of President John F. Kennedy and Jacqueline Kennedy Onassis went on to marry Carolyn Bessette in 1996. Three years later, the couple tragically perished in a deadly plane crash.

Before tying the knot, JFK Jr. was romantically involved with several A-listers, including Daryl Hannah, Brooke Shields and Sarah Jessica Parker.

Madonna, for her part, was married to Sean Penn from 1985 to 1989 and Guy Ritchie from 2000 to 2008. She also dated Jean-Michel Basquiat, Luke Perry and Tupac Shakur.