The royal rule that George, Charlotte and Louis will have to follow if they decide to get married

There are a number of rules that Prince William and Kate Middleton's three children - Prince George, Princess Charlotte and Prince Louis - must follow. The royal nanny has some strict rules for the Cambridge children, but they must also follow certain traditions, such as bowing to the Queen at this age.

As they get older, they will continue to adhere to protocol, and if they should decide to get married there's one restriction in place.

The Duke of Cambridge is second in line to the throne, meaning that George, Charlotte and Louis are third, fourth and fifth respectively, and due to the line of succession there's a very important rule in place when it comes to saying 'I do'.

As it stands, the first six members of the royal family in line to the throne must ask the reigning monarch for permission if they want to get married. Prince Harry, who is currently sixth in line, sought the Queen's approval before tying the knot in 2018, as did William in 2011.

The 1722 Royal Marriages Act meant that all members of the royal family needed the monarch's blessing to wed, but this has since been updated and one constitutional expert spoke to Express.co.uk about the impact this will have on the Cambridge children.

Iain MacMarthanne told the publication: '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.

'The 2013 Act sought to bring multiple pieces of outdated and discriminatory legislation relating to the monarchy up to date.'

He continued: 'Through this Act male primogeniture was abolished, allowing the firstborn child irrespective of gender to become heir apparent. The disqualification from inheriting the throne by marrying a Catholic was removed.

'And the Royal Marriages Act of 1772 was repealed, resulting in only the first six in line to the throne being required to obtain the sovereign’s permission.

'Consequently, should the children of the Duke and Duchess of Cambridge wish to marry, they will be required to seek the sovereign’s permission.'

So now you know!