Meghan becomes first Duchess of Sussex

Meghan's new royal title of Duchess of Sussex on marriage is "really rather wonderful", a historian has said.

Meghan Markle has become the first Duchess of Sussex. (AAP)

Meghan Markle has become the first Duchess of Sussex, a title one historian describes as "really rather wonderful".

The title has also only been used once before by Prince Augustus, who was Queen Victoria's favourity uncle, in the early 1800s whose wife was not given the title of Duchess.

Had Harry not been made a duke, Meghan would have become Her Royal Highness, Princess Henry of Wales - with her title incorporating her husband actual first name because she is not a princess in her own right. She would not have been Princess Meghan.

The prospect of taking on Harry's first name is not something Meghan, a former UN women's advocate, is likely to have wanted to do.

"She will become the first Duchess of Sussex," Clarissa Campbell Orr, visiting fellow at St Mary's University said:

"That's important because she would not be Princess Meghan, she would have been Princess Henry.

"If you are not born a princess then you take your title from your husband, your rank, from your husband."

Historian Hugo Vickers said "Princess Henry doesn't really work in modern times."

"The Duchess of Sussex is really rather wonderful."

Campbell Orr suggested that in everyday conversation, the royal bride is likely to still be referred to as Meghan Markle.