"I think it's very important for them to be there with her," Charles Spencer tells PEOPLE

By Simon Perry and Michelle Tauber
July 28, 2017 04:30 PM

On the anniversary of Princess Diana’s death, her brother reflected on his “final duty” to his sister.

The late princess is buried on the island of the Oval Lake at the family estate of Althorp, around 75 miles north of London. It is a bucolic spot that reflects her love of nature and water. “She’s in a happy and secure place,” Charles, 9th Earl Spencer previously told PEOPLE.

It is also somewhere that her sons, Prince William and Prince Harry, can visit peacefully.

Credit: Jonathan Beech

“I never go to Diana with them. It’s very much their time there,” said Spencer. “But I think I think it’s very important for them to be there with her. It is, luckily, very tranquil here and they can come and go as they wish whenever they want. And that’s very lovely for me to know that.”

Credit: Georges De Keerle/Getty Images

Last year, on what would have been Diana’s 56th birthday, William and Kate, their children Prince George and Princess Charlotte, Prince Harry and members of the Spencer family attended a poignant re-dedication ceremony at the recently renovated island, where rhododendrons and her favorite forget-me-nots have been re-planted.

Diana is also symbolically evident in the engagement ring worn by the daughter-in-law she never knew, Princess Kate.

“It’s lovely,” says Spencer. “I love the fact that there’s still such veneration inside her immediate family for what she was and what she meant . . . It shows what a good mother she was.”