Royal Wedding: What to Call Kate Middleton?

LONDON, April 29, 2011— -- Confused about Kate Middleton's title now that she's married? Is she a princess, a duchess, a countess or even a baroness?

Take your pick.

"Kate will automatically become the Duchess of Cambridge, the Countess of Strathearn and the Baroness of Carrickfergus now that she's married to William," royal historian Robert Lacey said.

The queen visited Cambridge a few days ago, sparking rumors that a dukedom might be in line for William.

Watch a special two-hour "20/20" tonight at 9 ET as Barbara Walters takes a look back at the royal wedding watched by the world.

As for Strathearn, it's the royal family's strong Scottish link. Strathearn has had royal connections since Robert Stewart, High Steward of Scotland, was created Earl of Strathearn in 1357.

And then there's the Irish title. Carrickfergus is County Antrim's oldest town. It is located on the north shore of Belfast Lough and is the site of Carrickfergus Castle, which dates from about 1180 and is one of the best preserved castles in Ireland.

"Technically, she will be 'Your Royal Highness' and most experts would say she is 'Her Royal Highness Princess William of Wales,'" Lacey said. "She may choose not to use the title but that is technically what she is.

"When William becomes the Prince of Wales, Kate will become the Princess of Wales, but not until then."

Technically, a woman must be born a royal -- think Princess Beatrice and Princess Eugenie -- in order to have the title "princess" precede her name.

"I think there is quite a chance that in the media, she will become Princess Kate or Princess Catherine," Lacey admitted. "It doesn't really matter as long as people love her."