Crown Princess Leonor of Spain, on her 18th birthday, took an oath of allegiance to the country’s constitution in a ceremony at the lower house of parliament in Madrid. If she succeeds her father, King Felipe VI, she will be Spain’s first female head of state since 1868. Princess Leonor was also set to receive Spain’s highest civilian honor, the Order of Charles III collar, at the Royal Palace. However, her controversial grandfather, former King Juan Carlos, was only invited to the private evening birthday celebration at the Pardo Palace. While many celebrated the event, it was boycotted by some political parties advocating for the monarchy’s abolition. Princess Leonor, who has begun military training, is expected to help bolster the monarchy’s popularity and stability alongside her father.