“They keep talking about respecting the Queen… well, words are cheap,” Robert told host Kate Thornton and fellow guests Angela Levin and Russell Myers.
“That entire interview did not respect the Queen. It did not respect the institution she has served for 75 years, for all of her adult life.”
He continued: “The monarchy and the crown, it’s not all about the royal family, it’s not all about the Queen, it’s part of our democracy.
“It’s almost as if they’ve burnt the American flag, or disowned the presidency – they’ve attacked the institution of monarchy. It’s not show business, it’s part of what we are.
“This is a gross insult to the British people in my opinion,” he added.
Broadcaster and royal author Angela Levin then weighed in on the matter, saying Brits consider the royal family as an extension of their own.
“People think of the royal family as part of their own family – an extension. They care about the baby, which is why we wanted to know when Archie was born.
“They care about people growing up, they see them, they are part of you, and to hear someone to come in and smash the lot of them, to be so forceful in their comments, it made me feel very upset,” she said.
Harry and Meghan's interview with Oprah airs tonight on Channel 10 at 7.30pm.