Princess Diana’s death devastated royal family fans worldwide when the limousine the royal rode on crashed in Paris in 1997. The event was especially devastating to her two sons with Prince Charles, Prince William, and Prince Harry, who were left without a mother at such a young age.

The Princess of Wales’ tragic death was especially devastating for her younger son Harry. “Without his mother, who died when he was twelve years old, Harry has had a really tough time,” Angela Levin wrote on “Harry: Conversations with the Prince,” according to New Idea.

In fact, Levin said that Diana’s untimely death drastically changed Harry’s personality almost overnight. From a sweet boy, the young prince got into smoking, drinking and has some problems at school.

“Her death changed Harry from being an adorable mischievous boy who was beginning to comprehend what it meant to be third in line to the throne and forever one large step behind his big brother, into a wilful impulsive pre-teen who, as he grew, behaved badly, rarely handed in his schoolwork on time, drank and smoked too much, and connected with too many unsuitable girls,” Levin said in her biography, according to Express.

But, while Diana’s death pushed Harry to change, it was also the memory of his mother’s love that brought Harry back. “His ongoing longing to please his mother and remain a good boy in her eyes is the primary reason he has come back from his personal abyss,” the author added.

Richard Kay, one of Diana’s close friends, revealed that while she loved both her sons, she “poured more love and attention into Harry” to compensate for the preferential treatment William received as the future king. “She adored them both but William, destined to be King, was marked from birth for special attention,” Kay said.

In her biography, Levin also revealed the most important thing Princess Diana did for Prince Harry. “He told me that the most important thing she ever did for him was ‘keep me safe,'” the Duke of Sussex told the author who also described it as “one of the many poignant moments” in their conversation.

Prince William, Princess Diana and Prince Harry Princess Diana (1961-1997) with her sons, Prince William (left) and Prince Harry, on a skiing holiday in Lech, Austria, 30th March 1993. Jayne Fincher/Princess Diana Archive/Getty Images