Prince William reportedly made a promise to his mom, Princess Diana, but could not fulfill it.

The Duke of Cambridge was only 14 years old when Princess Diana and Prince Charles got divorced. It was a difficult time for Prince William and Prince Harry.

As royals, the Prince of Wales and the People's Princess had to sort out her royal titles. Queen Elizabeth II was reportedly fine with Princess Diana keeping the Her Royal Highness title. However, the next-in-line to the throne was not. As a result, Princess Diana was stripped of the title, and Prince William and Prince Harry's mom had to curtsy to them.

Prince William was attending Eton College at the time. Despite his young age, he felt his mom's predicament and supported her emotionally. In fact, the duke reportedly made a promise to Princess Diana. "Don't worry Mummy, I will give it back to you one day when I am king," Prince William said, according to Paul Burrell in his book "A Royal Duty."

Unfortunately, Kate Middleton's husband never had the chance to fulfill his promise to Princess Diana. His mom died a few years later following their divorce.

According to Burrell, Princess Diana's former butler, the princess had a premonition of her death. She reportedly suspected that her ex-husband, Prince Charles, would plot an automobile accident to kill her and marry Camilla Parker Bowles.

"Her words were 'these next few months, are the most difficult months of my life. I fear my husband is going to kill me. In an automobile accident. With head injuries. In order that he can remarry,'" Burrell recalled. "That is spooky. She predicted her own death nine months before she died."

Although Prince Harry and Prince William were still too young when their mom passed away, they never forget her ways. In fact, the Duke of Cambridge has adopted her mom's parenting style.

"[William] can do all the things that he thinks are important for family life and make sure that his children have that loving, caring, fun home that his mother was trying to create," a source told People.

Prince William and Middleton filled their home with Princess Diana's photos. The Duke also talked about Princess Diana to his children.

"So, I do [when] regularly putting George or Charlotte to bed, talk about her and just try and remind them that there are two grandmothers, there were two grandmothers in their lives, and so it's important that they know who she was and that she existed," Prince William said.