John F Kennedy Junior romanced Madonna with his collection of Waterford Crystal glasses during the couple's secret getaways at the Kennedy compound, a new book reveals.
From arranging a rendezvous at the gym to turning up separately at celebrity bashes and media events, the famous pair were extremely cautious to prevent news of their affair being made public.
Details of their relationship only emerged for the first time last week with the publication of extracts from a new biography of the only son of the famous US president by author Christopher Andersen.
The book tells how Madonna "went after" JFK Junior, telling friends she believed an affair with him "would be nothing less than cosmic".
Kennedy eventually managed to get his superstar girlfriend alone at the Kennedy Hyannis Port estate, near Cape Cod in Massachusetts.
Andersen writes: "Inside the compound, they curled up by the fire, sipping daiquiris from Waterford Crystal glasses marked 'Caroline' and 'John-John'".
The specially engraved glasses were souvenirs from the family's first trip to Ireland after the assassination of his father in November 1963.
Almost four years later, Jackie visited Ireland for a month-long private holiday with her children. During the visit, the Kennedys stayed at Woodstown House in Co Waterford, a secluded country home where Jackie and her children went for walks along the beach nearby.
At the time, Jackie said she came to Ireland with her family to fulfil the wishes of her late husband, who enjoyed his visit to Ireland in June 1963 so much that he vowed to return with his wife and children.
More than 20 years later, at their Hyannis Port getaway, JFK Jr, or John-John as he was affectionately known, and Madonna shared cocktails from the Waterford Crystal glasses, "bundled up in sweaters and jackets and jogged on the beach".
The six-acre waterfront property is regarded as the "only place" the lovebirds could relax and "let their guard down". And with good reason too.
In The Good Son: JFK Jr and the Mother he Loved, the author examines the very close, and sometimes stormy, relationship between JFK Junior and his iconic mother.
When her son started dating Madonna in 1988, shortly after her turbulent marriage to actor Sean Penn ended, Jackie instantly disapproved.
Although John-John was "totally in awe" of the Material Girl, Jackie was clearly not a fan.
Mr Andersen writes: "There were many things about Madonna that rubbed Jackie the wrong way, not the least of which was her habit of thumbing her nose at Roman Catholic rituals. Across the globe she was being condemned as a heretic."
The blonde superstar was also an unwelcome reminder of her husband's blatant infidelity with Marilyn Monroe - the sex symbol Madonna often tried to emulate.
And Madonna fuelled Jackie's dislike even further when, on the day John brought her to meet his mother for the first time, the singer brazenly signed herself in the guestbook at the Kennedys' apartment as "Mrs Sean Penn".
The book also claims Sean Penn confronted JFK Junior over the affair when they met at a party in Robert De Niro's honour at the Tribeca Grill. When Kennedy went to introduce himself, Penn reportedly snarled: "I know who you are. You owe me an apology."
The Kennedy-Madonna affair soon fizzled out and John-John moved on to other conquests, including actress Sarah Jessica Parker, until he eventually settled down and married Carolyn Bessette.
Sadly, their love story came to a tragic end when they both lost their lives in a plane crash in 1999.