What can Meghan Markle expect as an American woman marrying into British aristocracy?
To find out, InsideEdition.com spoke to Julie Montagu, who is originally from Sugar Grove, Ill. She married Luke Montagu, Viscount of Hinchingbrooke and the son of the Earl of Sandwich, 14 years ago and now resides in London.
Even after all these years, she's still adjusting to her life in the U.K.
“Even to this day I’m very nervous,” Montagu told InsideEdition.com. "… but then I know that when I mess up, it’s OK.”
Montagu, who is known for her role in Bravo's "Ladies of London,” says she is happy Prince Harry is marrying an American and believes Markle is a perfect match for him.
With the new marriage, the viscountess has some advice for Markle before she weds her prince on May 19.
“It's gonna take Meghan a long time to get her head around that House of Windsor,” Montagu said.
Montagu admits she has witnessed "English snobbery" due to her American background.
Montagu met Luke 15 years ago as a single mom with two children and was not aware of his role until three months into their relationship.
"He had to sit on the 45-minute ferry over to explain to me that his family is basically the Earl of Sandwich family," she said.
She noted the differences between traditions and rules in England vs. that of America.
She says it is a rule to come down for breakfast dressed and ready to go, never in pajamas.
Another known rule is that the husband and wife never sit together at formal dinners; they must sit next to strangers and make conversation.
“You just sit down and then the first courses get served and you speak to somebody on your left," she explained. "And then you know that when the next course gets served you have to switch sides and speak to the person on your right."
Montagu says Meghan has most likely gone shooting with Harry on the weekends and knows about the daily tea practices.
Along with this, she believes Meghan will take part in elevenses, which is a break at 11:00 a.m. that entails drinking slow gin that, unlike the gin in America, is an alcohol that comes from a fruit and it is very colorful. After the gin comes hot tomato soup with vodka and sausages.
She also emphasized the long, country walks after digesting meals.
“Then you get done eating and everybody goes out, rain or shine, mostly rain, and going for these long English country walks all the time,” she said.
The biggest advice Montagu has for Markle is to just be herself.
“If she messes up, which she probably will — and it probably has already happened — just be like, 'Yup, that's me,'" she said.
She added: "Stay American."
"One of the most endearing qualities that she has to give to the Royal family is this… wonderful, infectious American enthusiasm," she said. "Stay American. Keep the American accent and keep being vocal about her passions."
Montagu says she looks forward to the wedding and cannot wait to be at Windsor Castle reporting on the celebration.
"I’m obsessed with both of them," she said.
Markle will join Montagu in the small collection of American princesses who also include Grace Kelly and Rita Hayworth.
"Million Dollar American Princesses: Meghan Markle" premieres Sunday, May 13 at 9 p.m. on the Smithsonian Channel.