She may be marrying Prince Harry, but those who wish to refer to Meghan Markle by her proper tile after she weds shouldn't refer to the former "Suits" actress as Princess Meghan.

Due to both an old rule in British Royal protocol, as well as Harry's placement in the line of succession for the throne, Markle cannot legally call herself a Princess, even though she is marrying a Prince.

According to the BBC, there is a rule in Britain that only those who have "royal blood" can refer to themselves as Prince or Princess and use their own name. The same rule applied when Kate Middleton, currently the Duchess of Cambridge, married Harry's older brother, Prince William, in 2011. Because she was also not of royal blood, she was unable to refer to herself as Princess Catherine.

However, the royal blood credence does mean that any children Harry and Meghan have can be referred to as Prince and Princess. William and Kate's children are referred to as Prince George and Princess Charlotte due to their royal blood, and the rule will apply when their third child is born in April 2018 as well.

While that rule plays a large part in why Markle cannot refer to herself as Princess Meghan, there is also the fact that her husband has fallen in the line of succession through the years, and likely won't ever become the King of England. His father, Prince Charles, will inherit the throne following Queen Elizabeth's death, and William will be the one to inherit the throne after him. However, his three children all now stand before Harry in that line of succession, and he will officially become sixth in line for the throne.

As for what title Markle may receive, it is most likely that like Kate Middleton, she will earn a Duchess title following her marriage, provided the Queen bestows a Dukedom on Harry. According to People Magazine after the royal engagement was announced, it is most likely they will be named the new Duke and Duchess of Sussex, though the same titles are also available for Clarence, Avondale, Connaught and Windsor.

"Unless they create a new title for them, I think the Duke of Sussex is the most likely title," Joe Little of Majesty Magazine told the publication. "Otherwise Meghan would be known as Princess Henry of Wales and people wouldn't not understand that these days. But they may surprise us."

Prince Harry and Meghan Markle There are legal reasons why Meghan Markle cannot refer to herself as Princess Meghan. Here she and Prince Harry are pictured at the official photo call to announce their engagement at The Sunken Gardens at Kensington Palace on Nov. 27, 2017 in London, England. Photo: Chris Jackson/Getty Images