The only daughter of the Prince and Princess of Wales is formally addressed as Her Royal Highness Princess Charlotte of Wales, but that title may change in the future.
Charlotte might be given the title of Princess Royal when Prince William succeeds to the throne, but that depends on a number of variables.

Photo: Getty Images
Prior to Princess Anne turning 70 on August 15, 2020, the royal family posted information about her life on their social media platforms. At the time, they tweeted: “HRH In 1987, The Princess Anne received the honorary title of The Princess Royal, which is traditionally given to The Sovereign’s eldest daughter. Following Princess Mary, the only daughter of King George V, HRH is the seventh Princess Royal.”

Princess Elizabeth was the eldest child of the reigning monarch George VI at the time, but because her aunt Princess Mary held the title, Princess Elizabeth was never referred to as the Princess Royal. Prince William will also be unable to give the title to his daughter Charlotte if Princess Anne is still using it when he succeeds to the throne.
Even then, the sovereign’s eldest daughter is not always given the title of Princess Royal. Princess Anne was only given the title of Princess Royal by the Queen in June 1987, despite the fact that it had been vacant since Princess Mary’s passing in 1965.

Princess Mary, the daughter of King Charles I and Queen Henrietta Maria, received the title of Princess Royal for the first time in 1642. It is said that Queen Henrietta Maria, who was the daughter of King Henry IV of France, wished to emulate the way the French monarch’s eldest daughter was addressed as “Madame Royale.”