This is the royal marriage law Prince Harry and Meghan's son Archie must follow

Prince Harry and Meghan Markle may have exited royal duties, but their son Archie may still be bound by a royal marriage law.

According to Express, although Archie does not have a royal title, his place in the line of succession means he may have to seek permission from the monarch to marry.

The 14-month-old is seventh in line to the throne, but once Prince Charles becomes King he will be sixth in line. The 2013 Succession of the Crown Act rule states those sixth in line and above must get the monarch's approval to marry according to a royal expert.

Iain MacMarthanne told Express: "Prior to the Succession of the Crown Act 2013 all descendants of George II, under the terms of the Royal Marriages Act 1772, unless the issue of a princess who had married into a foreign royal family, had to obtain the sovereign's permission to marry in order to retain their rights in succession.

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"The 2013 Act sought to bring multiple pieces of outdated and discriminatory legislation relating to the monarchy up to date."

While it is up to Archie to decide when he is 18 whether he wants to use the HRH title, MacMarthanne says he may still be bound by the obligation. This means Archie may have to follow the same rules as his young royal cousins Prince George, Princess Charlotte, and Prince Louis.

However, Archie will be free to marry without royal approval if Prince William, Duke of Cambridge, and Catherine, Duchess of Cambridge, have a fourth child.

"Should [Archie] marry, he will have to seek the sovereign's permission unless one of his three cousins marry and have children first, as he will be sixth in line when his grandfather is king," MacMarthanne explained.

When Archie grows up, Prince Charles or Prince William will most likely be king.

The Duke and Duchess of Sussex are currently settling into a new home in Montecito, California.

This article was first published on the NZ Herald and is republished here with permission.