As Cambridge is Prince William and Kate Middleton's assigned dukedom, that's the surname their children have been given.
Kate and William's children Prince George, Princess Charlotte and Prince Louis will be enrolled at school with the surname Cambridge, as their parents are the Duke and Duchess of Cambridge.
Since Harry and Meghan are the Duke and Duchess of Sussex, their children could use Sussex as a last name. But when Meghan and Harry's baby was born in May 2019, he was officially named Archie Harrison Mountbatten-Windsor. With no royal title he will be known as 'Master Archie.'
When Meghan Markle married Prince Harry in May 2018, her last name officially became 'Mountbatten-Windsor'.
But the British royal family are very rarely referred to by their last name, with those who marry into the monarchy often still using their maiden name.
Meghan Markle was granted the name Duchess of Sussex while her husband Harry is known as the Duke of Sussex.
What is the royal family's last name?
Because members of the royal family as so well known, they do not typically require a surname to be identified.
Before 1917, members of the British Royal Family had no surname at all, only the name of the house or dynasty to which they belonged.
What is the Queen's last name?
In 1901, when Queen Victoria, the last British monarch from the House of Hanover, died, her son Edward VII became the first British Monarch of the House of Saxe-Coburg and Gotha.
The name was changed from Saxe-Coburg and Gotha to the English Windsor, from Windsor Castle, in 1917 because of anti-German sentiment during World War One.
When the Queen Elizabeth II married Philip Mountbatten in 1947, it was thought the name 'Mountbatten' may become the royal family's new official surname. However, when Elizabeth's grandmother, Queen Mary, heard of this, she informed British Prime Minister Winston Churchill that the royal house was to remain known as the House of Windsor.
In 1952, when she succeeded the throne, the Queen officially announced that Windsor would be the royal surname, saying: 'My descendants, other than female descendants who marry and their descendants, shall bear the name of Windsor.'
This prompted Prince Philip to complain infamously that, 'I am nothing but a bloody amoeba. I am the only man in the country not allowed to give his name to his own children.'
In 1960 it was announced that Mountbatten-Windsor would be the personal surname applied to male-line descendants of the Queen and King George V without royal styles and titles.
'It was declared in the Privy Council that the Queen's descendants, other than those with the style of Royal Highness and the title of Prince/Princess, or female descendants who marry, would carry the name of Mountbatten-Windsor,' the Royal Family website reads.
Mountbatten is Prince Philip's surname and the name first appeared on an official royal document on November 14 1973, when Princess Anne married Captain Mark Phillips. And Prince Andrew, Duke of York, also used it on his wedding certificate in 1986.
Unless Prince Charles makes any changes when he becomes king, 'he will continue to be of the House of Windsor and his grandchildren will use the surname Mountbatten-Windsor', the website continues.
Mountbatten-Windsor differs from the official name of the British Royal Family which remains the House of Windsor.