In an emotional interview with BBC for an upcoming documentary, set to air this summer, the 34-year-old said he and Harry "owe it" to Di to keep her memory alive: "I think an element of it is feeling like we let her down when we were younger."
"We couldn't protect her," he continued. "We feel we at least owe her 20 years on to stand up for her name and remind everybody of the character and person that she was."
"Do our duties as sons in protecting her," William added.
According to the Daily Mail, Harry delivers an equally emotional account of Diana's death, recounting how overwhelming the ordeal was.
"When she died there was such an outpour of emotion and love which was quite, which was shocking," he said.
As Radar readers know, Princess Diana was killed when her limo crashed into a tunnel wall in Paris in 1997.
We pay for juicy info! Do you have a story for RadarOnline.com? Email us at firstname.lastname@example.org, or call us at (866) ON-RADAR (667-2327) any time, day or night.