THORNBURY, England - From curtsying to Queen Elizabeth to calling her "Your Majesty", US actress Meghan Markle will have to learn her royal lines when she marries Prince Harry and joins the ranks of the British monarchy.

Unwritten rules govern how the royals should behave and the public act around them. While many antiquated protocols have fallen by the wayside, there is still some etiquette Markle will be expected to follow after her wedding to the queen's grandson on May 19.

"The problem is that she's got to remember that, as a member of the royal family, she represents the family or, as it's been called, 'the brand'," said Grant Harrold, who served as a butler to Harry himself while working for his father Prince Charles, and now provides expert guidance on the subject.

"So, I think there is quite a lot pressure to make sure she gets it right because the last thing she wants to do is do something wrong or make a mistake and it ends up becoming front page news - and then it's embarrassing for her and for the royal family," Harrold said.

For someone who grew up in Los Angeles, life behind palace walls - where butlers, footmen and members of the royal household, often dressed in smart traditional uniforms with scarlet waistcoats, discreetly go about their jobs - could scarcely be more different.

Harrold says the formal protocol surrounding the royals, such as when to bow or curtsy, and to whom, and how to eat at royal banquets, was mostly set by the 17th century French king Louis XIV.

"Etiquette and protocol is really important to the royal family. It's been important to royals for centuries," Harrold said. "Those rules are there ... one - to make them understand what's expected of them, but also - so they understand what to do and what not to do."

Strict protocol also dictates that she should walk backward from the queen in her presence, although Harrold says you would not see this in public. But as the monarchy evolves and modernizes, these conventions are not as important as they once were, something the royals themselves acknowledge.

Those who breach the unspoken rules, however, can sometimes expect a frosty reception.

Last year, the governor general of Canada admitted breaking protocol by touching the queen's arm during an engagement in London and Australian Prime Minister Paul Keating was dubbed the "Lizard of Oz" by the British press after he appeared to put his arm around the monarch's shoulders in 1992.

Reuters