Meghan Markle is expected to become the Duchess of Sussex when she weds Prince Harry.
The American actress will become a fully fledged member of the royal family - with an HRH title to match.
Tradition dictates that royal men receive a title on the morning of their wedding - with Harry looking set to become the Duke of Sussex.
The prince is expected to be given a dukedom by his grandmother, the Queen.
Genealogist Charles Kidd said he believed the Duke of Sussex would be chosen for Harry, meaning Meghan would become Her Royal Highness The Duchess of Sussex.
"They're quite limited in the titles that are available. The Duke of Sussex is the front-runner without any doubt," he said.
"I think the others are highly unlikely. Clarence hasn't been used for a long time and it's been sort of tainted by bad luck.
"One Duke of Clarence was the eldest son of Edward VII and there have been a lot of fairly salacious stories surrounding him.
"Another Duke of Clarence was executed for treason and allegedly drowned in a butt of Malmsey wine.
"Connaught, with its links to the Republic of Ireland, might not be suitable at the moment.
"The dukedoms of Cumberland, Albany and Teviotdale are all suspended, meaning there could be claims to those titles."
Windsor - last used by the abdicated Edward VIII - is likely to be off the table.
Although it would reclaim the title for a new generation, Wallis Simpson - the last Duchess of Windsor, who sparked the abdication crisis of 1936 - was, like Meghan, an American divorcee.
Other options could include Avondale and Kendal.
Harry - whose full name is Prince Henry of Wales - could turn down a title, but would be a surprise move.
In this case, Meghan would be known as HRH Princess Henry of Wales.
She is not entitled to be Princess Meghan because she is not a princess in her own right, only through marriage.
The Duke and Duchess of Cambridge were also given titles linking them to Scotland and Northern Ireland, becoming the Earl and Countess of Strathearn and Baron and Baroness Carrickfergus, meaning Harry and Meghan might also be given multiple ones as well.