"The news hit him hard," explains royal author Tina Brown.
"He was worried about the fallout from the public, and the impact it would have on their sons."
She continued: "He was absolutely distraught. He fell apart. He knew, instantly, that this was going to be a terrible thing, that he will be blamed, that they (the Royal family) will be blamed, for the death of Diana."
When Diana died after a car crash in Paris, Prince Charles had to break the news to William and Harry.
"How you deal with that, I don't know," Harry, who was just 12 at the time, told BBC documentary Diana, 7 Days back in 2017.
"One of the hardest things for a parent to have to do is to tell your children that other parent has died."