Meghan Markle, the American bride-to-be of Prince Harry, has already become a global trendsetter with her bold sartorial statements.

Her personal style, which has been described as “California girl" and "effortless,” breaks the traditional fashion choices of British royals. The white coat by the Toronto-based brand "Line the Label" that Markle, 36, wore when she officially announced her engagement to Harry, 33, at Kensington Palace on Monday quickly sold out online that same day.

Britain's Prince Harry arrives with Meghan Markle for their engagement announcement at Kensington Palace, London, Nov. 27, 2017. (Toby Melville/Reuters) Britain's Prince Harry arrives with Meghan Markle for their engagement announcement at Kensington Palace, London, Nov. 27, 2017.

“This is the very beginning of this huge wave we’re going to ride in terms of Meghan and her popularity and fascination,” celebrity stylist Joe Zee said on “Good Morning America” today. “I think people are just going to be clamoring for more and more of this. I mean we saw those websites crashing from what she was wearing yesterday and she looked phenomenal. There’s such an accessibility about Meghan that I think girls in America particularly are going to be clamoring for her style.”

This September, the $185 dress by the Vancouver-based brand Aritzia that Markle wore when she attended the Invictus Games also sold out online shortly after photos of her at the event emerged.

Meghan Markle watches the opening ceremony of the Invictus Games in Toronto, Sept. 23, 2017.(Stephen Lock/ i-Images/Polaris) Meghan Markle watches the opening ceremony of the Invictus Games in Toronto, Sept. 23, 2017.

Some fashion writers have dubbed Markle's influence on trends the "Meghan Effect," similar to what has been called the "Kate Middleton Effect," in which consumers quickly snap up whatever the Duchess of Cambridge has been spotted wearing.

While both women have wielded immense power over retail trends, many have observed how the American actress' modern fashion choices contrast with Princess Kate's more conservative wardrobe.

“Between her and Kate, there’s something very regal and classic and sophisticated about Kate, and not that Meghan isn’t, but there’s almost this laid-back, Cali cool girl [feel] about her,” said Zee.

Britain's Prince Harry's fiancee Meghan Markle poses for a photograph in the Sunken Garden at Kensington Palace in west London on Nov. 27, 2017.(AFP/Getty Images) Britain's Prince Harry's fiancee Meghan Markle poses for a photograph in the Sunken Garden at Kensington Palace in west London on Nov. 27, 2017.

Markle's choice to bare her legs during her engagement announcement on Monday made headlines. Queen Elizabeth and Princess Kate typically wear tights or pantyhose in public.

“She didn’t wear stockings, which, in the royal handbook of fashion, it’s a big beginning of being a rule breaker in a way. I thought that was really great,” said Zee about the unspoken dress code kept by many British royals. “But even the green dress she wore, it was on the website with sleeves and she chose the sleeveless version.”

He continued, “There’s always a youthful spirit about Meghan, and there’s an ease. I think you also see that difference between William and Harry. There’s an ease about Harry.”

Markle described her personal sense of style as "California-girl" and "relaxed" in an interview during New York City Fashion Week in 2015 with Zee on Yahoo.

"I like to look polished and put together, but for me there's always going to be that effortless quality just coming from L.A.," Markle said.

"I think the most important thing you can do is tailoring," Markle added. "You think it's not going to make a big impact but if it fits you to a T, you look a million times better."

Actress Meghan Markle in New York, March 17, 2016.(Mireya Acierto/FilmMagic via Getty Images, FILE) Actress Meghan Markle in New York, March 17, 2016.

Last month, Markle's casual sense of style was on full display when she donned ripped denim and a loose button-down blouse while at the Invictus Games with Harry.

Prince Harry and Meghan Markle attend the wheelchair tennis event together at the Invictus Games in Toronto, Sept. 25, 2017.(Splash News) Prince Harry and Meghan Markle attend the wheelchair tennis event together at the Invictus Games in Toronto, Sept. 25, 2017.

While she now settles into her role as a trendsetter, Markle is no stranger to the fashion industry. In October 2016, Markle unveiled her own fashion line for the Canadian retailer Reitmans.

She shared a photo of herself modeling part of her collection on Instagram, including a faux-leather pencil skirt and a black turtleneck. In another photo for the brand, which features items in muted earth tones and mixes knit fabrics with silks and faux leather, Markle wore a pair of skin-tight pants.

ABC News' Carolyn Durand contributed to this report.