Princess Diana's Brother Charles Spencer Dishes on What Kind of Grandmother She Would Have Been

On the 21st anniversary of her death, Princess Diana's brother Charles Spencer is dishing on how he feels she would have been a wonderful grandmother.

Speaking to PEOPLE, Spencer — Diana's younger brother — said that the fact she would never get to meet her grandchildren was "one of the great tragedies...ever."

He went on to say that, while her death is no less tragic now than it was at the time it happened, he is very proud of the men his nephews Prince William and Prince Harry have grown into.

"I love seeing the sort of uncomplicated way that they deal with people, and put them at their ease," Spencer gushed. "It's so easy to connect the dots between them and their mother."

"What's amazing to me is the passing of time. Now William and Catherine are nearly the same age as Diana when she died," he added, spotlighting the fact that William, the Duke of Cambridge, is 36 years old, the same age Diana was when she was killed in a terrible car accident.

"I love the fact that there's still such veneration inside her immediate family for what she was, and what she meant," Spencer went on to say. "I think that's fantastic."

Regarding the tragic day that she passed away, Spencer says that he has always been preoccupied with the notion that maybe he could have done something to prevent it.

"I was furious, I wasn't just angry. [I thought] what could I have done. But you always think, God, I wish I could've protected her. It was just…it was devastating," he confessed. "I always felt…intensely protective towards her."

In the years after her death, Spencer became an outspoken advocate for the preservation of her memory in world history.

"One of the reasons I wanted to talk now is because I think after 20 years, someone shifts from being a contemporary person to a person of history actually," he explained. "And Diana deserves a place in history."

"I think that it's important for people who are under 35, who probably won't remember her at all, to remember that this is a special person," Spencer finally said. "Not just a beautiful one."

Diana died on Aug. 31 1997, when a car she was traveling in crashed in the Pont de l'Alma tunnel in Paris. Two other passengers — Diana's partner Dodi Fayed and the driver Henri Paul — were also killed, but Diana's bodyguard Trevor Rees-Jones survived the crash.