It has been 20 years since Princess Diana tragically died. Now, her two sons Prince William and Prince Harry have once again opened up to the public to share their memories of their beloved mother -- even though they vowed that they would never speak about the matter again.

In HBO's documentary about Princess Diana, entitled, "Our Mother: Her Life and Legacy," it aims to introduce the People's Princess to a new generation. The movie shows some up-close-and-personal moments, as well as moving confessions.

Touching moments from the documentary

Per Vanity Fair, here are some of the best moments that can be seen in the Princess Diana documentary:

William on being Diana's son: According to Prince William, it was devastating to lose someone very close to him at an early age, although he still considers himself lucky to have known his mother for 15 years.

William added that he still thinks about Diana everyday.

The final phone call: One of the movie's most heartbreaking moments is when William and Harry first publicly disclosed their final phone call with their mother. At that time, they were on holiday with Prince Charles' family. Diana called from Paris but they did not have much time to speak. Prince Harry said that he can't really recall what they talked about but confessed that he regretted how short the phone conversation was, adding that he has to deal with that for the rest of his life.

William on "introducing" his children to his late mother: In one scene, William was asked how he keeps his mother's memory alive now that he has children of his own.

He said that he does this by talking about Grandma Diana. He added that there are many pictures of her around the house. Although, sometimes it's hard because, since Kate (Duchess of Cambridge) did not know her, she can't really give a lot of details to George and Charlotte.

Buckingham Palace exhibit

Meanwhile, also in line with the commemoration of Princess Diana's 20th death anniversary, Buckingham Palace visitors will be treated to an exhibit this summer.

They can view some of the late princess’ most treasured belongings -- including her music collection and ballet shoes. According to Reader's Digest, the exhibit was put together by none other than Diana’s sons, Princes William and Harry. They chose the objects for display, hoping to reflect their mother's steadfast dedication to her duty and their own personal memories of her. The exhibit will run until October 1, 2017.