It was that comment, Nicholl says, that drew Harry's family's attention, particularly that of his brother, Prince William, and father, Prince Charles.
"I think the problem with the podcast and the things Harry has said -- particularly about the institution, feeling like he was in The Truman Show, feeling like he was in a zoo -- it has echoes of what he said on Oprah, that he, and his brother, and his father feel trapped by the institution," Nicholl explains. "It may be how Harry feels, but I don't think it's how William and Charles feel."
Harry also expressed discontent with his childhood, saying that he wanted to "break" the cycle of "genetic pain and suffering" with his and Meghan's children, Archie, 2, and a daughter on the way.
"There's no blame. I don't think we should be pointing the finger or blaming anybody. But certainly when it comes to parenting, if I've experienced some form of pain or suffering because of the pain or suffering that perhaps my father or my parents had suffered, I'm going to make sure that I break that cycle so that I don't pass it on," he said. "There's a lot of genetic pain and suffering that gets passed on anyway. We as parents should be doing the most we can to try and say, 'You know what? That happened to me. I'm going to make sure that doesn't happen to you.'"
The apparent criticism of Charles has not been received well by the family or the U.K. in general, Nicholl says.
"Prince Harry prefaced what he said with saying that he wasn't trying to point the finger. He didn't want this to be reduced to a blame game, but his comments are quite personal," Nicholl says. "He talks about a cycle of pain, he talks about genetic pain. The interpretation of that is that he wanted to break that cycle of pain that he recognized within his own family relationships."
"It does seem that this is yet another example of Prince Harry criticizing the royal family, in particular his father, who of course came under some fire in that Oprah interview," she adds. "... I think there is that sense again that he feels he's been let down by his father in this interview. That's going to be incredibly hurtful for the Prince of Wales."
Additionally, a source tells ET that Harry's comment about feeling like he was living in zoo was "hurtful" to many members of the royal family, who feel he "shouldn’t be complaining."
The source adds that "the family is distressed and angry" over Harry's latest interview, noting there is great concern that these remarks are coming so soon after Prince Philip’s funeral when Harry had joined with the family in a show of unity to support the queen.
A second source says there is :confusion why private matters are being discussed so publicly when this is one of the things Harry objected to so much himself."
Nicholl additionally points out, "When Prince Charles was asked if he was aware of his son's podcast today on an engagement, he pointedly refused to answer."
When it comes to the brothers' relationship, Nicholl believes that Harry's recent comments may play a negative role.
"I think it's inevitable that every time Harry speaks out about personal family relationships, it is going to be damaging to the healing of this rift, particularly between William and Harry," she says. "I think there is a desire on the part of both of the brothers to move on, to try and heal this relationship. The problem is, when Harry sits down and gives a really personal interview like this... it really does set back that healing process."
"Of course, everyone is wondering, will the brothers be standing should by shoulder on July the first for the unveiling of the Diana statue? What's that body chemistry going to look like?" Nicholl wonders. "At the moment, we're still not a 100 percent sure that Harry is going to be here for that statue unveiling. Of course, a lot of it depends on when his daughter is born and how Meghan is."
As for the country itself, Nicholl says that Harry's comments left the U.K. in "quite a bit of shock" that the duke "went as far as he did."
"I think certainly people over here are a little disappointed and I think frustrated as well, hearing Prince Harry indirectly criticize the royal family, which I think is the interpretation by some over here in the U.K.," Nicholl says. "... I think there's a feeling over here in the U.K [that] no one has a problem with Prince Harry talking about mental health. I think most people think it's an important campaign [and that] raising awareness about it can only be a good thing... but a lot of people here think Prince Harry has overstepped a mark in talking so personally about his father, and his relationship with his father, in what most people have interpreted to be quite a critical way."
Nicholl adds that the perception of Harry's comments is different in the U.K. and the U.S. "I think certainly stateside there is a lot more sympathy for Prince Harry than there is here over in the U.K.," she says.
While it's unclear if Harry has spoken to members of the royal family since the podcast aired, Nicholl believes that the duke's comments may slow the progress of any reconciliation.
"I think it goes without saying that clearly some of the things that he has raised in this podcast have been hurtful to the royal family, I think particularly for the queen and Prince Charles, who are very private when it comes to their personal emotions," Nicholl says. "This idea of Harry venting, airing publicly, his private grievances is going to be problematic."
"I think it does raise the really important issue of trust. I know Prince Charles is really keen to get his relationship with his youngest son back on track... He's prepared to work with it, but that issue of trust is one that concerns him as much as it does William," she adds. "They want to know that the conversations they are having are going to remain private, and they want to know that these conversations are worthwhile, and that they are making progress."
Overall, the interview, Nicholl believes, "really just opens up yet another Pandora's box, only set that healing process back 10 steps."
"I think Harry knows that [the royals] are not going to respond to this," Nicholl adds. "They really have been rendered voiceless and, to a degree, quite powerless, but I think there is always, of course, two sides to every story."
Despite the potential disappointment from his family, Nicholl believes that "Prince Harry was very pleased with the podcast, very pleased to have that platform to reach out, particularly to a younger audience."
"My understanding from Prince Harry's team is that he is pleased with how it's been received, certainly in America, and that he predicted and anticipated there would be this type of backlash in the British press," she adds.
Even with any backlash, Nicholl notes that the podcast interview will not be the last time Harry and Meghan discuss royal life or mental health.
"They are going to do everything they can, I think, to keep that spotlight on the importance of mental health," she says. "I was not surprised that Prince Harry is going to podcast about his mental health. I was surprised to hear how far he went with some of what he said, but... I think we should all be expecting to hear more of him about this conversation."
"It is something that he is passionate about. He clearly believes in it. He believes he can make a difference," Nicholl adds. "I think, unfortunately for the royal family, Prince Harry is not afraid to draw on his own experience in order to relay the importance of mental health and get his message out."