When she married her prince back on 2011 Kate Middleton became the Duchess of Cambridge.
Along with Prince William, the couple have been known by their official titles ever since, and their children George, Charlotte and Louis have also taken on their title.
But like many other things in the royal family, this will change when the Queen dies .
William and Kate will get new titles to represent them moving up the line of succession.
At the moment, Prince Charles is the Prince of Wales.
This title isn't just his, it's the title which is traditionally given to the heir to the throne and Charles is the 21st man to be given it.
Diana became the Princess of Wales after she married Charles in 1981.
Technically, Camilla should now have the title but she turned it down out of respect for Diana.
But after the Queen's death and Prince Charles becomes king, Prince William will become the Prince of Wales and Kate will probably be offered the title of Princess of Wales.
It probably wouldn't have gone down well with the public if Camilla took the title, but it's a very different situation with Kate.
She might decide she wants to use the name as a tribute to the mother-in-law she never met.
Until Wills, Prince Harry won't get a new title when his grandmother dies as he is much further down the line of succession.
When he married Meghan Markle earlier this year, the Queen gave them the titles the Duke and Duchess of Sussex.
Even though the Duke title has been used before, Meghan is the first Duchess of Sussex because of a rather upsetting course of events surrounding the original.
The original was Prince Augustus Frederick, the son of George III born in 1773.
He was university educated and campaigned for the abolition of slavery.
He married twice, but his father George III didn't approve of either and ruled they were unlawful.
This meant his wives were never given the Duchess title, and his children were not consider heirs to the throne.