Author of “Ladies’ Man: The Careless Heart of John F. Kennedy” Was ‘Shocked’ By What He Learned — See the Cover! (Exclusive)

You’ve never seen John F. Kennedy like this before.

Bestselling biographer Laurence Leamer, author of Warhol’s Muses, Hitchcock’s Blondes and Capote’s Women — which was adapted into FX’s Emmy-nominated Feud — turns his pen to JFK in a new book publisher G.P. Putnam’s Sons calls “the most intimate and unsettling version of Kennedy’s life yet.”

Ladies’ Man: The Careless Heart of John F. Kennedy draws on decades of original reporting and interviews with more than 300 people connected to the Kennedys, including women who have never told their full stories before. What results is “a portrait of a charismatic, reckless and deeply conflicted man whose private behavior mirrored the risks he took with power,” the publisher teases.

But Leamer initially resisted writing the book. “What ultimately compelled him was not gossip, but time: revisiting interviews, transcripts and private testimony, and recognizing how much truth had been softened or left out in more reverential biographies,” the publisher adds.

The book will reveal “the harrowing, intimate life of JFK,” according to an official synopsis. “From JFK’s youthful indiscretions at boarding school, his early connections with such beautiful aristocratic European women as Inga Arvad and Gunilla Von Post, his marriage to the stately Jacqueline Bouvier, his affairs with Pamela Turnure and Diana de Vegh, his liaisons with mafia moll Judith Exner and East German spy Ellen Rometsch, to his relationship with Marilyn Monroe before her death, JFK’s affairs were multifaceted and often tragic.”

“His cautious public persona contrasted sharply with his reckless personal life, where he took bewildering chances that could have destroyed him. And as JFK’s profile rose, so did his rashness,” the synopsis continues.

“My very early readers who have read Ladies Man say they will never think about President Kennedy the same way again,” Leamer tells PEOPLE in an exclusive statement. “Having previously written three bestsellers about the Kennedys, I knew and interviewed three of JFK’s mistresses, as well as his brothers, sisters and closest friends and associates. But even I was shocked by some of the things I learned.”

“On his 46th birthday in May 1963, he was on the presidential yacht, USS Sequoia, with Jackie Kennedy on board, and the president literally chased Tony Bradlee, his close friend Ben Bradlee’s wife, around the boat to make a pass at her,” Leamer adds. “He was that out of control.”

The synopsis promises that “Ladies’ Man reframes the romanticized glamour Camelot through the women who knew JFK best — lovers, confidantes and casualties of his private life. Their stories reveal how power functioned behind the scenes, and who paid the price for maintaining the illusion.”

It will also offer “a striking psychological reframing of JFK’s compulsive womanizing, connecting it to his lifelong illnesses and fear of mortality — sex as proof of vitality, and as a way to outrun pain,” the synopsis adds. “It’s a portrait of masculinity built on denial, risk, and compulsion—one that feels newly relevant now.”

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Ladies’ Man will hit shelves on Oct. 20 and is available for preorder now, wherever books are sold.