Inside King Charles' Secret Life Behind Palace Doors

Less than 12 hours after Diana Spencer died in a car crash in 1997, her ex-husband, King Charles, arrived at a Paris hospital to take her body home.

"When he saw Diana, the head nurse said, it looked like he had been struck in the face by an unseen force. Everybody thought he was going to collapse. Later, he was sobbing openly," said Christopher Andersen, author of the new biography The King: The Life of Charles III.

Charles rose to the occasion following Diana's death by convincing his mother, Queen Elizabeth II, to fly flags at half-mast and show the respect that his ex-wife justly deserved.

Twenty-seven years later, King Charles, 75, faces an even greater challenge: To overcome his eccentricities, self-doubts and unresolved hurts, and unite his country under his reign.

"He's a very complicated, complex and paradoxical figure," explained Andersen. [But] he is really chomping at the bit to make his mark on history."

Elizabeth and Prince Philip's eldest child was, of course, born to rule, but his life hasn't been easy. Ignored by his busy parents and bullied by his classmates, Charles endured a very lonely childhood.

"Philip sent him to one of the roughest private schools. All night long, the other students would hit him in the head and kick him," Anderson detailed, noting Charles' letters home, pleading to be transferred to another school, went unanswered.

His parents did not even visit when Charles nearly died at age 13 from a ruptured appendix. His sole sources of affection within the royal family came from his grandmother, the Queen Mother, and Mabel Anderson, his nanny, who was also the only one allowed to mend the prince's beloved teddy bear.

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"She is still alive and still close to the king," revealed Andersen.

King Charles had to learn how to control his volcanic temper and constant complaints.

"One time he lost a cuff link down the sink in the bathroom, and he tore the sink off the wall," spilled the author, claiming Charles has also been known to throw things and lash out at his valet.

Luckily, his wife, Queen Consort Camilla, has learned to placate him.

"She kind of sets him straight," Andersen shared. "She will take him aside and say, 'You are king. Nobody wants to hear that. Do not complain.'"

Charles is trying because after a lifetime on the sidelines, he's ready for his moment.

"Anybody who thinks that Charles is just keeping the throne warm for [Prince] William is very mistaken," said Andersen. "If the monarchy flourishes, he will be the reason. If the monarchy crumbles, he will be the reason. So all eyes are on Charles III."