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Meet The World's Royal Teenagers

3. Princess Leonor Of Spain
Princess Leonor, who is 15 years old, is the teenage daughter of King Felipe VI and and Queen Letizia. She is their oldest child and the heir presumptive to the throne. While she is currently first-in-line to the throne, she is an heir "presumptive" because if her parents had a son, she would be bumped to second-in-line.

According to People, she will make history as the first Queen Regnant since the 19th century. The last Queen Regnant was Queen Isabella II, who reigned from 1833 to 1868. Since it seems unlikely the king and queen will have more kids, Princess Leonor is already a ruler-in-training — the young princess already gave her first public address on her 13th birthday.