"Cillian didn't respect his privacy," another joked.
Harry's struggle with being the son of King Charles and the younger brother of Prince William became the focal point of his scathing memoir, Spare. The Royal Observer previously reported His Majesty refused to read the bestseller because he believed his child's words were "hurtful."
Harry received criticism for discussing the Prince of Wales' looks in the opening chapter.
"I looked at Willy, really looked at him, perhaps for the first time since we were little, taking in every detail: his familiar scowl, which had always been the norm in his dealings with me," the former military captain wrote.
"His familiar scowl, which had always been his default in dealings with me; his alarming baldness, more advanced than my own; his famous resemblance to Mummy, which was fading with time," he added.
While promoting Spare, the veteran defended his project.
"I don’t see it as cutting at all," Harry told Anderson Cooper.
"My brother and I love each other. I love him deeply. There has been a lot of pain between the two of us, especially the last six years," he added. "None of anything that I've written, anything I’ve included is ever intended to hurt my family."