Yes, there is at least one prominent 18-year-old princess as of late 2023/early 2024.
Princess Leonor of Spain
Princess Leonor of Spain, the heir to the Spanish throne, turned 18 on October 31, 2023. To mark this significant milestone, she swore allegiance to the Spanish Constitution before the Spanish Parliament in November 2023. This formal act highlights her commitment to her future role as head of state.
Therefore, Princess Leonor serves as a direct answer to the question.
