Madonna and JFK Jr. had an affair in the late 1980s, and Jackie O was not happy about it. 

As superstar Madonna celebrates her 60th birthday, many famous and fabled stories from her life have been popping out of the woodwork, including accounts of her alleged affair with JFK Jr. 

An affair his mother Jackie was not happy about. 

According to the 2014 tell-all book  "The Good Son: JFK Jr. and the Mother he Loved" by Christopher Anderson, in 1988, the same year JFK Jr. was named the Sexiest Man Alive by People magazine, he and the Material Girl began a steamy affair. 

Read More: The story behind that famous photo of Marilyn Monroe with JFK and RFK

Jackie and JFK Jr.

Jackie and JFK Jr.

Madonna had recently split from - but had not yet divorced - Sean Penn, and Kennedy was reportedly still with his girlfriend at the time, actress Cristina Haag. 

According to Anderson, they had met three years earlier during a party after one of Madonna's Madison Square Garden concerts, and after her split, she decided to go after John Jr. 

Being two very famous people, they kept the alleged tryst under wraps, meeting at the same gym or jogging around Central Park incognito. 

Read More: Caroline Kennedy's son looks exactly like JFK Jr. 

They even cozied up with some Waterford Crystal: 

"The only place the superstar couple could let their guard down was in Hyannis Port, where they bundled up in sweaters and jackets and jogged on the beach. Inside the compound, they curled up by the fire, sipping daiquiris from Waterford crystal glasses marked "Caroline" and "John-John" — souvenirs from the family's first trip to Ireland after the assassination."

But when Kennedy took Madonna to his mother's apartment at 1040 Fifth Avenue, she was not impressed. 

Apparently, she signed the guest book as "Mrs. Sean Penn," and Jackie, who was Catholic, found her use of Catholic symbols and icons in her music videos and performances to be offensive. 

Then there was also the whole Marilyn Monroe thing: 

"One unwelcome reminder of JFK's torrid affair with Marilyn — the affair that most troubled Jackie — arrived on her doorstep in the form of another blond bombshell by the name of Madonna. Already a pop icon, Madonna was best known at the time for her 'Material Girl' video, an homage to Monroe's 'Diamonds Are a Girl's Best Friend' number from the film Gentlemen Prefer Blondes."

Much to Jackie's relief, we imagine, the affair fizzled out, and JFK Jr. wed Carolyn Bessette in 1996.

Tragically, the couple perished with Bessette's sister Lauren when the light plane Kennedy was piloting crashed off the coast of Martha's Vineyard on July 16, 1999. 

Read More: JFK Jr.'s last interview - moving words on Jackie and President Kennedy

Madonna and JFK Jr. Wiki Commons