Princess Leonor, was born on October 31, 2005, as the Infanta Leonor de Borbón y Ortiz (via The Irish Times). Her parents are Their Majesties King Felipe VI of Spain and Queen Letizia, per the Spanish royal family. At the time of Leonor's birth, Felipe was crown Prince of Spain, aka the Prince of Asturias. It was only when Felipe ascended in 2014 that Leonor became a princess. Because of the circumstances under which her father came to reign (the abdication of his father and predecessor, King Juan Carlos), Princess Leonor shares with Her Majesty Queen Elizabeth II the unusual distinction among European heirs to the throne of being alive contemporaneously with both the current sovereign and the former (via Brittanica).
All other children and grandchildren of the monarch are born with the title Infante or Infanta, depending on their gender assignment at birth (via Britannica). At the time of Leonor's birth in 2005, her father, then-crown Prince Felipe, was not the monarch, but rather, the heir apparent to his father, then-King Juan Carlos. Accordingly, at birth, Leonor was known as HRH Infanta Leonor and had to wait until her father ascended the throne in 2014 to use the princess title. Her younger sister, Sofia, was also born HRH Infanta and remains as such, even now that her father is king.
The Spanish title of prince/princess is exclusive to the person next in line to the living monarch, per El Pais.
Accordingly, when Leonor's father, Felipe, became king on June 19, 2014, Leonor's title changed automatically from Infanta Leonor to Princess Leonor of Asturias. She also holds the titles of "Princess of Girona and Princess of Viana, corresponding to the firstborn of the Kingdom of Castile, the Throne of Aragon and the Kingdom of Navarre, whose union formed the Spanish Monarchy in the 16th century," as well as the Duchess of Montblanc, the Countess of Cervera, and the Lady of Balaguer, according to the Spanish royal family website.
