'King Charles: The Boy Who Walked Alone' Claims Princess Diana Cheated First

'King Charles: The Boy Who Walked Alone' premieres May 2 on Paramount+.

Just ahead of the coronation of King Charles III, an upcoming documentary is shedding new light on the early years of the British royal, his complicated relationships and the "spectacularly dysfunctional" royal family.

King Charles: The Boy Who Walked Alone premieres May 2 on Paramount+, and offers intimate new interviews with some of the people who knew the king when he was still the Prince of Wales, including goddaughter India Hicks, former chef Mervyn Wycherley, former classmate Johnny Stonborough, squadron leader Graham Laurien, former girlfriends Janet Jenkins and Jane Ward and more.

"I'm speaking now because I've said nothing for 40 years, and I've listened so often to lies," says Allen Peters, a former royal protection officer, in ET's exclusive first look at the upcoming doc.

"We have never seen King Charles in such an intimate, personal, emotional way," says Susan Zirinsky, president of See It Now Studios. "This documentary will leave viewers with an all-new understanding of what influenced his life and how he got to be the person he is today. You will never look at him the same way again."

See the first look at the doc below:

From the sensitive boy growing up in the shadow of his mother's distancing devotion to duty and his father's machismo and bullying, to the young playboy sending love letters to girlfriends, to the unhappily married heir to the throne, The Boy Who Walked Alone paints a complicated picture of one of the most visible men in the world.

"He's actually one of the most emotional people I've ever met," shares biographer Catherine Mayer.

The documentary also shares previously unreported details about the king's relationship with the late Princess Diana, and how they continue to impact his relationship with Prince Harry.

"I can categorically say that the first person that strayed in the marriage was the Princess of Wales," claims Allan Peters, Former Royal Protection Officer.

King Charles: The Boy Who Walked Alone premieres May 2 on Paramount+.

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