A veteran royal journalist has lashed out at Prince Harry and Meghan Markle for continuing to use their royal titles for publicity and money.

The Duke and Duchess of Sussex may have quit their royal duties and no longer represent the monarchy for over two years, but this has not stopped them from using their royal titles in their charity work and public engagements. The most recent example was their appearance at the United Nations General Assembly, where the 37-year-old delivered a speech about climate change and world hunger, among others.

Royal author Duncan Larcombe called the couple's behaviour "unacceptable." He criticised their continued use of their royal titles to promote themselves in the U.S.A. and even branded them as "royals for sale."

"Harry and Meghan are royals, but they are royals for sale and there's no getting away from it," he told Closer magazine adding, "In terms of the Palace, that is what is unacceptable about their behaviour."

He accused the couple of capitalising on their ties to the British monarchy as he continued, "You're taking one of the most established brands and you're lining your pockets in the U.S. with it."

Larcombe, who wrote "Prince Harry: The Inside Story," expressed his sadness at what the Duke of Sussex has become after he married the former "Suits" actress and moved with her to California.

"It's sad because he was so loved. And the Royal Family work together and support each other. He is making a difference to people's lives, but he was before [he left]," he shared.

The author has been outspoken in his disapproval of the Duke and Duchess of Sussex. He even warned of "another world of pain" for the royals if the couple decides to go on a second Oprah interview to talk about the bullying allegations against the duchess.

Larcombe's criticism of the Duke and Duchess of Sussex came after they attended the United Nations General Assembly on Monday, July 18. The 37-year-old gave an impassioned speech in which he warned of a "global assault on democracy and freedom" and delved into U.S. politics.

Prince Harry and Meghan Markle were met with protests when they arrived at the U.N. There were those who questioned why they were invited when they live in a nine-bedroom mansion in Montecito.

Prince Harry, Meghan Markle Oprah interview
Prince Harry, Meghan Markle sat down with Oprah Winfrey to talk about their experience as senior working royals. CBS Mornings/YouTube