Amid Meghan Markle's feud with the British royal family, a Hollywood screenwriter has made sensational claims about her behaviour during her days as an American actress.

Royal historian Robert Lacey has quoted the Los Angeles-based screenwriter in his new book "Battle of Brothers," which details the feud between Meghan's husband Prince Harry and his elder brother Prince William. The source claimed to Lacey that the "Suits" alum "does not cope well with what she perceives as rejection" and can become "remorseless" if she doesn't get what she wants.

"She's nice and smiley as can be until you step in her way or don't give her what she hopes for. Then she can be remorseless – heaven help you!" the insider claimed.

Lacey points out Meghan's possible display of such behaviour in his book. It has been claimed that the Duchess of Sussex had cut short her visit to a Fijian market in October 2018 after seeing UN Women posters, because they had reportedly snubbed her years before by assigning her a "lesser role" of advocate instead of goodwill ambassador.

The British royal was reportedly annoyed at her aides for taking her to the engagement where UN Women were advertised. Lacey claims that a CCTV camera has captured her turning to speak to an aide in a way "that made the younger woman's face blanch."

Another footage showed her being escorted away by security guards after she whispered to a bodyguard. At the time, it was said that the royal who was pregnant with her first child had to abruptly end her walkabout because the crowds grew too big to control. However, Lacey says the sudden departure may have been because the Duchess had "caught sight of promotional material advertising UN Women."

At the High Commissioner’s Residence The Duchess of Sussex met leaders advocates and role models from across Fijian society — including people involved in women’s empowerment. #RoyalVisitFiji

— The Duke and Duchess of Cambridge (@KensingtonRoyal) October 24, 2018

The former actress had previously received a standing ovation at UN after she gave a keynote address in front of notable guests including secretary-general Ban Ki-moon on gender equality for UN Women in New York in 2015. Lacey claims that she had hoped to become a prominent figure in UN Women and was disappointed when things did not go that way for her.

"[Meghan] had rubbed shoulders with the likes of Hillary Clinton... and might have hoped to join UN Women's distinguished roster of goodwill ambassadors that included celebrities such as Nicole Kidman and Emma Watson... but in those pre-Harry days UN Women only assigned the cable actress the lesser role of advocate," Lacey wrote.

He cited another source who claimed that Meghan had said she would only visit the Fiji market if there was no branding for UN Women, but "snapped" after seeing posters and T-shirts advertising them. However, lawyers for the mother-of-two denied the claims and said that she had even met with leaders from UN Women later during her visit.

Meghan Markle
Then-actress Meghan Markle attends the Annual Charity Day Hosted By Cantor Fitzgerald And BGC at the Cantor Fitzgerald Office on September 11, 2013 in New York, United States. Getty