Jackie Kennedy couldn't dial down her emotions after this phone call.

In J. Randy Taraborrelli new biography Jackie: Public, Private, Secret, the author compiled almost 25 years of research and interviews with her family, friends and former lovers into an in-depth portrait of the former First Lady. As such, it inevitably touches upon her husband President John F. Kennedy's alleged affair with Marilyn Monroe, which Taraborrelli claims consisted of a weekend-long fling in March 1962.

In fact, the book also details a brief but affecting phone call between Kennedy and Monroe one month after the Gentlemen Prefer Blondes star's affair with the then-president. So, what happened during the exchange?

Taraborrelli notes in the book that in April 1962, Kennedy received a phone call to her bedroom from Monroe while at the family's Hyannis Port, Massachusetts residence. The actress, whose distinctive voice was recognizable to Kennedy, had been calling looking for "Jack," prompting the First Lady to verify that it was Monroe calling. This prompted the Seven Year Itch star to reply, "Is this Jackie?" before asking if Kennedy could pass on a message to her husband that she had called. However, Monroe noted that she only wanted to say hi.

And as Taraborrelli put it, a stunned Kennedy said she would pass the message along before hanging up. However, the brief exchange, which according to the author occurred just four months before Monroe's death, left Kennedy with a whole lot of questions.

"There was something about that phone call," the biographer told Fox News July 18. "She later told family members that there was a haunting quality to Marilyn's voice that really stuck with her. And it's not like they even had any kind of deep conversation. But it was 10 years of wondering, was it really Marilyn Monroe? And that buzz stayed with the family."

Per the biography, Kennedy later described Monroe's voice during the conversation as having a "sad" and "ethereal, little-girl-lost quality," which she found to be "disturbing." And according to Jackie: Public, Private, Secret, it remains a mystery how Monroe even obtained the number—the bedroom was the only phone line in the house in which calls weren't intercepted by the Secret Service. 

It was just one month after the phone call that Monroe performed her now-infamous rendition of "Happy Birthday" to JFK during his 45th birthday celebration—from which the First Lady was notably absent.

Following Monroe's death at age 36 that August, Tarborrelli noted to Fox that while Kennedy was "bereft" by Monroe's untimely death, she also always felt the star to be a "disaster waiting to happen," and "someone too vulnerable, too weak to be played with by JFK."

However, he also said she ultimately understood her husband. As he put it to the outlet: "Her main concern was JFK. She knew what it took to be with a very powerful man. And great men like JFK have great flaws."