He was American royalty and she was the beauty he chose as his wife.
On the surface, JFK Jr. and Carolyn Bessette were a perfect match.
Now, an explosive new book, Fairytale Interrupted, says they were trapped in a tempestuous and unhappy marriage.
Terenzio told ABC's 20/20 she was an unlikely confidante of JFK Jr. and Carolyn.
"A girl from the Bronx, not a lot of fancy education or privilege meets John F. Kennedy Jr., the most famous person in the world. That's not likely," Terenzio says of her linking up with Kennedy.
Terenzio became the couple's mediator.
"I always seemed to be playing referee. They were both too stubborn to work things out on their own," Terenzio writes in her book.
A lost video, shot weeks before their 1996 marriage, displays how volatile their relationship was.
They appeared in love as they walked John-John's beloved dog, Friday, in New York's Central Park. Then a furious argument erupted.
Carolyn chased after JFK Jr and lunged at him. The fight got physical. He struggled with her and took away her engagement ring.
The fight continued as they sat on a park bench feet apart. Carolyn seemed to be shouting and crying.
Later, exhausted and heartbroken, JFK Jr. sat on the sidewalk, his head bowed as the harangue continued.
He gave her back the engagement ring, but he got angry when she tried to take his dog.
Moments later, they were passionately hugging and making up.
Terenzio says those fights usually happened because JFK Jr. was "Insensitive, clueless and disorganized."
Carolyn's biggest complaint was that John Jr. ignored her. "I'm not a priority. It's always something else," Terenzio writes of Carolyn's issues in the book.
Terenzio told 20/20 she feels guilty over Carolyn's death.
She had refused to go with her husband to a Kennedy cousin's wedding after yet another fight, until Terenzio stepped in.
"Carolyn, are you **** kidding me?" Terenzio said to Carolyn, "What are you doing? You're smarter than this. His whole family is going to be at this wedding and you need to go with him. Go get a dress and I'll get you a car to the airport," Terenzio ordered Carolyn.
Hours later Carolyn, her sister Lauren and JFK Jr. were killed when their plane crashed into the ocean off Martha's Vineyard.