On the day of the funeral of Diana, princess of Wales—a sunny Saturday in September 1997—there was one small item that broke a million hearts in a city, and a nation, already awash in grief. A bouquet of white freesias sat atop her coffin as it rode on a gun carriage to Westminster Abbey. Nestled in the flowers was an envelope with a single word—“MUMMY”—printed in a child’s hand. Walking behind were its authors, princes William, 15, and Harry, 12, accompanied by their father, Prince Charles, their grandfather, Prince Philip, and their embittered uncle, Charles Spencer, Diana’s brother. At the time, those of us covering the funeral, and millions more watching on London’s streets and on televisions around the world, wondered what these wounded young lads could possibly have said to make sense of the tragedy that befell their mother, and the circus of grief it spawned.

That note also touched a deep chord with Penny Junor, a veteran royal watcher and the author of the newly published Prince William: Born to be King, which manages to be both a sympathetic portrait of the future king and a controversial examination of an upbringing that was scarred by tumult, loss and Diana’s mental fragility. “I thought it was incredibly touching,” she said of the note. It was only through the wise intervention of Sandy Henney, Prince Charles’s press secretary at the time, that the boys’ farewell words to their mother were sealed in an envelope, protected from the reach of the hundreds of telephoto lenses lining the funeral route. “Their lives had been so intruded upon by the media,” Junor said in an interview with Maclean’s. “That would have been the end of their world if their little note to their mother had been picked up by those lenses.”

In fact, the privacy of William and Harry’s lives had been trammelled from birth. Long before their mother’s death, they endured the loss of loved ones who fell out of favour with their parents, and the rage, tears and public humiliation of the marriage breakup that left them caught between the warring camps of mother and father. “He would be superhuman if he didn’t have demons,” Junor writes of William. “But he keeps them to himself; he is one of the most intensely private people you could meet.”

The release of her book in Britain last week triggered a storm of controversy due to Junor’s assessment of Diana as a loving mother, but one whose mental illness caused enormous pain to her children. Her claim has generated a storm of criticism from a pro-Diana camp that remains steadfastly loyal almost 15 years after her death. This week, Hasnat Khan, the Pakistani heart surgeon who had a two-year relationship with the princess that ended shortly before her death, spoke out in her defence. “There is no way at all that Diana was mentally unstable,” he told the Mail on Sunday. “There is nothing wrong with expecting your husband to be faithful, and being angry when he isn’t.”

Yet by Diana’s own admission, she suffered from bulimia, cut herself on her arms and legs, and made half-hearted attempts at suicide. “I can’t understand how people got so hysterical about it,” Junor said. “Anybody who understands eating disorders, anorexia, bulimia, they are serious mental illnesses. I’m a trustee of our national charity for eating disorders, so I do know how dangerous these things are. People die of them.” Junor said she could have gone further. A psychologist she consulted said Diana exhibited narcissistic tendencies. “That’s exactly what she was, but I thought the word [narcissist] would be so inflammatory. God, what would the Daily Mail have done with that?”

Junor made similar claims about Diana’s mental health in a book, Charles: Victim or Villain, published a year after Diana’s death. “I had death threats. I was nearly run out of the country. People spat at me in the streets.” Briefly, she hired a bodyguard. Even today, “there are people who can’t accept who she was,” Junor said. “She was wonderful in many ways. I’m absolutely not wanting to desecrate her memory, but the facts are William had a very difficult time growing up.” Her latest book casts Charles in a more sympathetic light, as a sensitive, caring parent and as a worthy future monarch. But both parents, in her view, have much to answer for in the rearing of their sons.

William as a young child rightly earned Diana’s affectionate nickname as “Your Royal Naughtiness.” Junor described William, age 4, wandering into a meeting his father was having with Bob Geldof, the perpetually scruffy singer and humanitarian. “Why do you have to talk to that man?” William asked. “Because we have work to do,” Charles replied. “He’s all dirty,” said William. “Shut up, you horrible boy,” said Geldof. “He’s got scruffy hair and wet shoes,” William said, undaunted. “Don’t be rude,” was about all his mortified father could muster. Both parents were soft touches when it came to discipline. It was the Queen, a doting grandmother and latter-day role model, who signalled that young William’s behaviour was unacceptable.

The marriage was already in trouble by the time of Harry’s arrival in 1984, some 27 months after William’s birth. Charles grew frustrated and depressed as he failed to win the respect and support of his young wife. Diana had wild mood swings: carefree and compassionate one moment, brooding, insecure and sarcastic the next. Much of it, Junor believes, was rooted in Diana’s difficult childhood. Her home life was marked with unhappiness and there were frequent violent arguments between her parents. Her mother fled the marriage for another man and lost custody of the children when Diana was six. “In [Diana’s] mind, the matter was simple,” Junor writes. “Her mother didn’t want her, therefore she must be worthless.”

For all the love Diana showered on her boys, her insecurities were never far from the surface. Barbara Barnes was the children’s beloved nanny. Each morning William would climb into bed with her before they got up for breakfast. Diana began to feel threatened by William’s bond with Barnes, and the nanny was dismissed on the flimsiest of excuses. William, just 4, was hurt and bewildered at the loss of his “Baba,” as he called her. “He became less outgoing, less trusting, less inclined to make himself vulnerable,” wrote Junor. Over the phone from London, there is an edge of anger in Junor’s voice. “The only explanation is she was so tied up with her own feelings that she couldn’t look beyond them to see what this would do to her sons,” she said. “It’s so weird, given that she herself was abandoned and knew how painful that was.” Notably, nanny Barnes was one of the names William added to his personal wedding guest list 24 years after she vanished from his life.

Charles for a time was something of a stoic punching bag as the marriage disintegrated. Diana would rearrange the boys’ schedules to take away his custody time, while tipping photographers to the boys’ visits to, say, a water park—trading their privacy for chances to cast herself in a good light. She went to war against Tiggy Legge-Bourke, a fun-loving young aristocrat the boys adored and who often minded them under Charles’s watch. Diana started false rumours she was sleeping with Charles. In this case, she failed to get Legge-Bourke fired.

Diana didn’t hide her distress from the boys. She told a TV interviewer the tale of William at 10 playing a parenting role as she wailed inconsolably behind a locked bathroom after a fight with Charles. William crouched outside, saying, “I hate to see you sad,” and stuffed paper tissues under the door. “She gave away her children’s privacy,” said Junor. “It was extraordinary, absolutely extraordinary. If she was sane, if her mind had been totally fine, I don’t believe she would have behaved in the way she did. I think it was all a symptom of her condition.”

Things got worse with the boys away in boarding schools. Both parents turned to sympathetic media figures to tell their stories, and neither came off well with their cringeworthy tales of angst and infidelity. Charles did his best to guard the boys’ privacy and to speak respectfully of their mother. However, in a 1994 documentary by Jonathan Dimbleby seen by 14 million people, and in a subsequent book, he admitted to his infidelity with Camilla Parker Bowles after the marriage “was irretrievably broken.” William was 12. Life the next day in boarding school must have been hell.

A year later, Diana responded with a devastating interview on the TV program Panorama. It was here she talked about her bulimia and self-harm, suggested Charles was a dubious prospect as king, admitted to an infidelity or two, and fired that memorable broadside across Camilla’s bow: “There were three of us in this marriage, so it was a bit crowded.” Diana had to be prodded to travel to Eton, where 13-year-old William had recently enrolled, to tell him in advance that the program was running. “She told William that [it] would contain nothing controversial and that he would be proud of her,” Junor writes. William watched the program in the study of his Eton housemaster, angry, aghast and no doubt humiliated at the family secrets she laid bare before some 20 million viewers. Shortly afterwards the Queen told the warring couple to get on with a divorce. Sensing a deep need, the Queen encouraged William to make regular visits to Windsor Castle, just across the bridge from Eton, for tea and sympathy. The bond they already shared has only grown stronger in the years since.

It is little wonder that William grew increasingly insular, never quite certain who to trust, who might abandon him, who might betray what little privacy he had. Harry was the one constant: the brother who experienced the same losses, sorrows, humiliations, and the undeniable love both parents lavished on them. “Only they had experienced the full nightmare of life within the Wales household,” Junor writes. “Only they had known what it was like to be at an all-boys school when the newspapers were full of their parents’ infidelities; only they had known what it was like to grieve for their mother while millions of strangers took ownership of her death.” As young adults, when his and Harry’s cellphone messages were hacked in the News of the World scandal and used as fodder for stories, the brothers reacted with predictable rage, but also a measure of relief. They knew with final certainty that the media leaks were not coming from their tight circle of friends.

Perhaps understandably, the William who arrived at the University of St. Andrews in Scotland was cautious, insecure and a bit bereft. He hid under the bill of a baseball cap, was unduly quiet in lectures, often wrote his essays at the local police station, away from prying eyes, and steered clear of the American girls who threw themselves at his feet. He gravitated to familiar faces in his residence, among them Kate Middleton, one of the “least pushy girls he met in that first year,” Junor writes, quoting a friend of the couple. She, too, was away from her family and comfort zone. Like him, she had volunteered in Chile during her gap year with the same charitable group, though at different times.

By second year he felt comfortable enough with Kate and two other friends to share an apartment together, and his confidence grew after seriously questioning in first year if he would drop out. It was sometime during that year that their romance blossomed, a secret they kept for a remarkably long time, until a photographer captured a stolen kiss between them during a ski holiday. While Kate was obviously the prime attraction, the fun-loving Middleton family in semi-rural Berkshire offered a welcoming middle-class normal that was new to William. There were no butlers, no lurking photographers, Junor writes. They could grab a pint at the pub, “and they clattered about the kitchen and sat down to chatty, friendly, family meals together.”

As much as William found a home with the Middletons, it would take eight years, and one brief breakup with Kate in 2007, before he asked her to marry him. William did not agree to be interviewed for Junor’s book (although he gave permission for friends, staff and many of the charities he is patron of to share their views), so she can only speculate about his commitment issues. Part of it, she believes, was a question he had to resolve for himself: could he remain faithful to one woman after the betrayals that scarred his upbringing? She also admitted to “playing amateur psychologist.” He lost his nanny, he lost the trustworthy Sandy Henney when she was forced to resign as press secretary for a mistake not of her making. His mother’s death was the “ultimate abandonment,” said Junor. “I think he was possibly testing Kate to see if she would also abandon him. I think that’s why he waited eight years before finally asking her to marry him.” She did not. During their breakup, she maintained her dignity and discretion, while looking stunning as she stepped out on the town with friends. William soon realized what he had lost.

Junor was among the journalists who followed William and Catherine on their first official visit to Canada last year. Three decades earlier she’d watched Charles and Diana’s first visit to Wales as a married couple. Both women had a rare gift of putting an adoring public at ease. But that’s where the similarity ends. In William and Catherine she saw a connection, and a trust that Charles and Diana never shared. There were whispered asides and secret smiles, he guided her through events with a protective hand on her back. “There was such obvious love between the two of them,” she said.

With one woman, and perhaps the Queen, he can let down his guard. His model is his grandmother, who shares her private self with only her spouse. She knew what William learned from the painful experience of his parents: if you allow it, a fame-obsessed world will feed on you until you’re picked clean. As he approaches his 30th birthday on June 21, he sees himself not as a celebrity, but as a future monarch, in for the long haul. He has a duty to give his time, talent and energy, said Junor, “but he won’t give his soul.”

In many respects that MUMMY note, written at a time of aching loss for the young princes, is a metaphor for the man William has become. He can walk before millions behind his mother’s coffin, or into the enthusiastic embrace of a Canadian crowd, but we’ll never really know what he keeps sealed inside. And why should we?