- Meghan Markle and Prince Harry are expecting their first baby.
- In British nobility, you are only declared a prince or princess at birth if you are born to a sitting monarch, are the first-born son of the eldest son of a sitting monarch, or are otherwise declared to be so by a sitting monarch.
- Since Prince Harry is not the eldest son of the Prince of Wales, any of his children will officially be Lord or Lady Mountbatten-Windsor at birth - according to current rules.
- Sitting monarchs can issue Letters Patent, which can change the titles and styles of members of the royal family for the term of that monarch's reign.
- The Queen has previously issued such a patent for the children of Prince William and Kate Middleton.
- However, it is as yet unclear whether she will do the same for Prince Harry and Meghan Markle.
The new royal baby is expected in spring 2019, and will be seventh in line to the British throne - jumping in above newlywed Princess Eugenie - but it is uncertain at this stage what its title will be.
Here's everything we know so far.
How the titles currently work
When Prince William married Kate Middleton in 2011, she officially became"Her Royal Highness, Princess William of Wales." Similarly, Meghan Markle is now "Her Royal Highness, Princess Harry of Wales." They are not, however, officially known or called Princess Kate or Princess Meghan because they are not of "royal blood."
Long before Prince Harry was even a thought, his great-great-grandfather, King George V, limited the titles that members of the royal family could hold.
According to The Independent, A Letters Patent introduced by King George V in 1917 read, "...the grandchildren of the sons of any such Sovereign in the direct male line (save only the eldest living son of the eldest son of the Prince of Wales) shall have and enjoy in all occasions the style and title enjoyed by the children of Dukes of these Our Realms."
This means that as the first-born son of the first-born son of the Prince of Wales, Prince George (son of Prince William and Kate Middleton), is the only one of the Queen's grandchildren to be directly entitled to the title of Prince.
As it stands, any of the Duke and Duchess of Sussex's offspring will be known as either Lord or Lady Mountbatten-Windsor, a surname decided by Queen Elizabeth II and Prince Philip in 1960.
However, when it was announced in 2012 that Kate Middleton was pregnant with a second child, the Queen issued a Letters Patent under the Great Seal of the Realm, which ensured that all of the Duke and Duchess' children would receive the title of Prince and Princess.
"All the children of the eldest son of the Prince of Wales should have and enjoy the style, title and attribute of royal highness with the titular dignity of Prince or Princess prefixed to their Christian names or with such other titles of honour," the patent read.
Only time will tell whether Her Majesty will take similar action for the children of Prince Harry and Meghan Markle.