Despite the fact that the baby's first cousins are princes and a princess, the Sussex's son won't receive a royal title unless granted one by the Queen.
In 1917, King George V passed a Letters Patent, which stated that "...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 only enjoy in all occasions the style and title enjoyed by the children of Dukes of these Our Realms".
This means that Prince Harry and Meghan's son will likely not become a prince or known as "His Royal Highness", and may instead be known as Lord (forename) Mountbatten-Windsor.
The royal couple may choose to forego a title for their son altogether, in which case he may be known as Master (first name) Mountbatten-Windsor.
However, the Queen could issue a new Letters Patent to change this, as she did for the Duke and Duchess of Cambridge's children.
In December 2012, the Queen issued a Letters Patent under the Great Seal of the Realm declaring “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”.
This explains why Prince George, Princess Charlotte and Prince Louis all have HRH titles.
Another title that the Sussex's baby may receive bears links with an ancient Scottish kingdom.
On the day of the royal wedding in May 2018, one of the subsidiary titles Prince Harry was bestowed by the Queen was Earl of Dumbarton.
As the son of a duke, the baby is entitled to be known as this title.
Before Prince Harry was granted the title by his grandmother, it had not been used for more than 260 years.
The town of Dumbarton in Scotland, founded in the fifth century, was once the capital of the ancient Kingdom of Strathclyde.
According to Historic Environment Scotland, Dumbarton Castle in the region was a "mighty stronghold in the Dark Ages".
Legend dictates that the fort was visited by the wizard Merlin, from Arthurian legend, in the sixth century.
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