William's father King Charles III announced their new titles in a nationally televised speech Friday, his first as king.
"Today, I am proud to create him Prince of Wales, Tywysog Cymru, the country whose title I have been so greatly privileged to bear during so much of my life and duty," Charles said in a prerecorded speech. "With Catherine beside him, our new Prince and Princess of Wales will, I know, continue to inspire and lead our national conversations, helping to bring the marginal to the centre ground where vital help can be given."
William and Kate, the who have three children, are now the first couple to use the Prince and Princess of Wales titles since they were used by Charles and the late Princess Diana, who divorced in 1996.
Charles's current wife, Camilla, never used the title the Princess of Wales, going by the Duchess of Cornwall instead. She is now the Queen Consort with Charles' accession to the throne.
In taking on the Princess of Wales title, Kate "appreciates the history associated" with it, a royal source told ABC News.
The source added Kate though will "understandably want to look to the future as she creates her own path."
William, now heir to the throne, also assumes Charles' title of the Duke of Cornwall and inherits the duchy of Cornwall, the private estate that was established in 1337 to provide financial independence for the heir and his family.
"As my heir, William now assumes the Scottish titles which have meant so much to me," Charles said in his speech Friday. "He succeeds me as Duke of Cornwall and takes on the responsibilities for the duchy of Cornwall, which I have undertaken for more than five decades."
Kate, formerly the Duchess of Cambridge, inherits the new title of the Duchess of Cornwall.
William and Kate, along with their children Princes George and Louis and Princess Charlotte, recently moved from Kensington Palace to Adelaide Cottage, a four-bedroom cottage on the grounds of Windsor Castle.
This week, George, Charlotte and Louis attended their first day of school at Lambrook School in Berkshire, a preparatory school for children ages 3 to 13 in South East England.