Paul Burrell claims Princess Diana's name was "taboo" in Buckingham Palace after she passed away.
The former butler - who worked for the late royal until her untimely death in August 1997 - says Buckingham Palace was a "sterile and very cold world" in the months after.
Speaking on ITV's Lorraine, he said: "We have to remember that the boys [Prince William and Prince Harry] were 15 and 12 and they were taken into Buckingham Palace, a sterile and very cold world where Diana's name was taboo. They were never allowed to speak about her or talk about their emotions.
"Now they're not in that world and they're out of that system and they're young men with their own destiny in front of them so they can speak quite raw and candid about life inside Kensington Palace."
Meanwhile, Paul recently revealed he hasn't spoken to Prince William and Prince Harry in 20 years but praised them for continuing their mother's "hopes and dreams".
He said: "I haven't spoken to them since their mother died in 1997. But I'd love to speak to them. And I'd love to tell Catherine about the incredible woman who changed all the rules to make her life more comfortable. To give her a better life as a royal. It's what Diana did.
"I don't know why [they haven't contacted me]. But think about the system. The whole establishment is up against me because I'm the outsider. I belong in Diana's world. I'm the one who got away. You've never heard me say anything disrespectful about the royal family or the Queen. We have a wonderful monarch ... long may she reign ...
"I think they [Prince William and Harry] are wonderful. They are following in their mother's footsteps. She had them for long enough to instil her hopes and dreams and ideals. They are now the product of Diana."