While Meghan Markle became a princess of the United Kingdom when she married Prince Harry in 2018, those expecting her to dress like one have so far been largely disappointed.

Markle is certainly eligible to wear one, as royal etiquette dictates you can do so if you either were born a princess or married into the royal family.

The accessory is common among the duchess' peers. For instance, her sister-in-law, Kate Middleton, has been spotted wearing Princess Diana's Lover's Knot tiara to multiple events, most recently to a state banquet with US President Donald Trump and at a recent Buckingham Palace reception.

Insider spoke with the royal commentator Richard Fitzwilliams, who explained that Markle hadn't worn the accessory again because she hadn't had the opportunity.

Britain's Queen Elizabeth II and US President Donald Trump in the Music Room ahead of a State Banquet in the ballroom at Buckingham Palace. ALASTAIR GRANT/AFP/Getty Images

"Tiaras are worn by royals at weddings, state banquets, and other white-tie events," Fitzwilliams said.

The media speculated on why the duchess didn't wear a tiara to the state dinners she attended in Fiji and Tonga last year, with the Mail Online reporting that Prince Charles had advised her against wearing one as it could be seen as "too extravagant."

"Meghan did not understand all of this because she was new to the role and so Prince Charles told her that it would not be appropriate," a source told the publication.

"The dress codes at the Tonga and Fiji dinners were more relaxed in line with the personal preferences of Harry and Meghan in their tour of Oceania," he said. "At both Harry wore black tie. It would not have been appropriate for Meghan to wear a tiara at either."

Despite the strict rules surrounding when the royals get to wear tiaras, that doesn't mean we won't ever see the duchess wear one.

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"She will undoubtedly wear them at appropriate future events," Fitzwilliams said, "though obviously this will depend on the duties she and Harry decide they want to undertake as senior royals."

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