Report: Prince William made a heartbreaking promise to Princess Diana when she lost her royal title

Princess Diana's divorce from Prince Charles in 1995 can be counted as one of the year's biggest headlines. Following high-profile affairs from both sides of the marriage, scandalous interviews and a separation, divorce was inevitable. To avoid more drama, the queen reportedly wrote to Diana and Charles individually, asking them to divorce as soon as possible.

Prince Charles remained the Prince of Wales. Meanwhile, Princess Diana had her title stripped away.

While Queen Elizabeth was happy for her former daughter-in-law to keep her title, Prince Charles was reportedly not on board. And thus, Di was no longer to be referred to as "Her Royal Highness," further ostracizing her from the royal family and requiring her to "curtsey" to her sons.

RELATED: 9 shocking secrets about the people's princess

In return, Prince William, just 14 at the time, vowed to restore Princess Di's royal title, according to her former butler, Paul Burrell. "Don't worry Mummy, I will give it back to you one day when I am king," Burrell claims Will had promised his mother in Burrell's book "A Royal Duty."

Unfortunately, she passed away just a few years later.

The book has been well received by many readers, who commended Burrell on omitting "nasty" gossip from his biography. Burrell, who was friends with Diana for many years, strived to portray Diana in the most honest light, from her role as as a young mother and member of the royal family.

"He truly admires, respects, and even loves Princess Diana, so this is not a book filled with scandal and tabloid dirt," wrote one book reviewer. You can purchase Burrell's book here.

PHOTOS: Princess Di with Prince Charles together