When Prince Charles and Princess Diana ended their marriage in 1996, their oldest son, Prince William, was just 14 years old. At the time, he was a student at Eton College studying biology, art history, and geography and playing soccer and water polo. He hadn't yet begun his official royal duties or military career. For all intents and purposes, he was a normal teenager — besides, you know, the whole being king one day thing — and most normal teenagers are pretty bummed about their parents splitting up. But as second in line to the British throne, William recognized his (future) power and made a promise to his mother that is both incredibly adorable and incredibly heartbreaking.

Charles and Diana's divorce was finalized in August 1996, but some drama surrounding her royal title ensued. Queen Elizabeth II reportedly wanted to let Diana keep the style of her royal highness, but Charles was "adamant" that she give it up — instead, she was given the title Diana, Princess of Wales. The loss of the honorific separated Diana from the rest of the family in such a way that she had to curtsy to those who had it, including her own children. William is said to have comforted his mother after the loss of her title by saying, "Don't worry, Mummy, I will give it back to you one day when I am king."

Tragically, Diana was killed in a car crash just a little over a year after William made his touching vow to her. In the decades after her death, both he and his brother, Harry, have opened up about their mother, sharing stories about their time with her as well as honoring her impact, both with the charities they support and the traditions she's passed on to them.