Meghan Markle was given a dire warning by a royal commentator who urged her to "follow the example" of other American women who married into royalty in the past and managed to "remain dignified".

The Duchess of Sussex found herself in hot water recently following a new wave of negative publicity after Princess Diana's biographer and ex-Vanity Fair editor Tina Brown accused her of having "the worst judgment of anyone in the entire world".

Ms Brown, who's been critical of the Sussex couple before, gave out a scathing verdict on Meghan's decision-making and claimed that "all her ideas are total crap".

She told The Ankler podcast: "The trouble with Meghan is that she has the worst judgment of anyone in the entire world. She’s flawless about getting it all wrong. All of her ideas are total crap, unfortunately."

Now another biographer, Christopher Wilson, took aim at the duchess and suggested that following the latest negative reports, she should focus on leaving a "good mark on the world".

He wrote in a piece for the Mail: "Slammed by ex-Vanity Fair editor Tina Brown as having 'the worst judgment of anyone in the entire world', Meghan Markle, the Duchess of Sussex, appears to be attracting yet more negative publicity.

"So maybe this is the moment for Meghan to follow the example of the thirty-plus American women who married into royalty in the past – those who remained dignified and left behind a good mark on the world."

The author went on to list a number of American women who married into royalty and "achieved more in life with their royal marriages than Meghan Markle has so far managed", including the "most fabled of all" Grace Kelly, Princess of Monaco, Marie-Chantal, Crown Princess of Greece, Rita Hayworth, who was married to Prince Aly Khan from 1949-1953.

He also mentioned more "recent American princesses" like Kelly Rodesvedt, who married Prince Hubertus of Saxe-Coburg-Gotha in 2000 and Sarah Butler, who married Prince Zeid bin Ra'ad of Jordan in Amman also in 2000.

However, Mr Wilson added that Meghan could not be placed at the bottom of the list, with one last American woman taking the spot.

Barbara Hutton, an American socialite and granddaughter of retail tycoon Frank Winfield Woolworth was notoriously famous for her troubled private life.

She was once dubbed "Poor Little Rich Girl" and was at some point considered one of the wealthiest women in the world.

Barbara married seven times, with her fourth marriage in 1947 being to Prince Igor Troubetskoy, a French-born Russian prince who filed for divorce in 1951 and Prince Pierre Raymond Doan Vinh, a Laotian antique dealer who was an adopted member of the former royal family of the Kingdom of Champasak. Their marriage lasted two years and they divorced in 1966.

Mr Wilson wrote: Obituaries of her - after her 1979 death from a combination of drink, drugs, and diet pills - described her as a philanthropist, and in a manner of speaking, she was. She threw her money away at any passing man."